Ok so I know there are a couple of other posts but Here is my situation I have an 8 year old spayed bitch maltese she has always been a little aggressive toward strangers and barks at other dogs but is fine with my golden retriever ( a neutered male)... I got a female yorkie puppy and now she is 2 years old and is not spayed.
The Yorkie has become extremely aggressive toward my maltese. Does anybody know what to do?

Sounds like your Yorkie bitch is trying to be top dog!  Bitch bitch aggression is v. difficult to deal with.  Hopefully someone who knows more about behaviour will be along soon to help.

Sarah.

As your Yorkie has now reached maturity she is trying to change her status.  These things rarely happen out of the blue what has been preceding these fights and it is rare for there to be just one of them at fault but a conflict between the two. 

As you say the Maltese is not sociable has she perhaps bullied, in maybe subtle ways the Yorkie up to now, and now the Yorkie has matured she won't put up with it any more?  Yorkies are terriers and usually the dog in charge in mixed breed households that I know, with the toehr dog depending on breed letting them be boss.

I agree that terriers usually have a stronger drive to be in charge, how does your maltese react when this happens? Does she fight back, submit or ignore?

Your Yorkie will naturally be the alpha or try to be as she is is not spayed . I wouldn't Interfere with them, let them sort it out. If we make the judgement that the older dog is top [as she is your first baby] it can cause more situations for the Yorkie to challenge her. If your older girl is laid back then feed the younger girl first, give her treats first then she will not feel the need to hassle & fight her  she'll assume she comes first in your eyes . I was very shocked to find my 7 month puppy bitch dominated my older bull terrier but as he's male he let her without a fight. I'm sure if he had been a she there would of been fights too.

Not sure I would advice no interference, bitch on bitch fighting can lead to death and if the younger bitch has recently or is about to have her season I would be concerned that she may damage the older bitch and or even pick a fight with the castrated male.

Think the only way in this situation is to either spay and hope that does the trick although it may not or to re-home. I have had a similar bitch on bitch situation and had in the end to re-home the younger bitch as in the domestic situation it is impossible to keep the two warring dogs apart nor is it acceptable to live in a home when a fight may start at any moment, in the end it may lead to people being bitten and that can't continue.

In my case the older bitch was happy to let the younger take over and would avoid looking at her and sit facing the wall but it did not stop the younger setting about her when of course she would defend herself.

This is not a situation of a puppy play fighting with an adult dog this is serious matter of an out and out dog fight IMO

I generally do not interfere with the dogs minor issues nor do I deliberately set one up as above the others.  I expect them to get on, so who thinks who is in charge is irrelevant I will not tolerate any bullying or deliberate upstaging and intimidation tactics.

When I feed or give treats or attention, I decide who gets what first and the others must wait their turn.

When there have been power shifts in my gang I allowed them to happen as long as the usurper or usurper were using peaceable methods, no bullying or pushing out tolerated, no way.  Any argy bargy regardless of who starts it both get a telling off, as in the end it is I who am in charge.

I have had two lots of obvious power shifts, on both occasions a granddaughter with grandmother.  In the first instance it was for top canine, and in the second it has just recently been for second.

They demonstrate their superiority by staying slightly aloof from the others, and making it obvious that they are only deigning to play/associate with the lower ranks, LOL.

Before you go down any drastic routes (spaying/rehoming) as have been suggested, have you tried to just study their behaviour for a few days, and see whether you can see what behaviour comes before the fights. Then try intervening and chastising them at that point, rather than only noticing and seperating them in fight mode. Looking for any niggly, aggressive stances or pushing each other about, or even excited looking behaviour, and calmly reprimanding them for that might stop it escalating into fights.

Hopefully Barbara and R Reeve are correct and you will be able to sort this situation all I urge you to do it not to ignore and let them get on with it, this is the advice when a puppy is concerned but this is an adult dog and the situation needs to be looked at with the utmost care.