Hamsters fighting, help?

They do that. I have a chinese dwarf who was given to me by my cousin because he had to be separated from his brother because they were going to kill each other fighting. Once they reach a certain age they do seem to get more territorial, the pet store should have warned you about this possibility when you got them. You will have to separate them into different cages or one of them will be killed. Mine was around a year old when he started fighting too. It is kind of like puberty I think but they dont get over it like people do. It will just get worse.

Even when young hamsters are introduced or hamsters that have been living together moved to a new environment they may squabble and/or chase each other at first but the squabbling often sounds worse than it actually is and is just their way of establishing who is the boss in their new environment. During this process there may be much squealing and chasing but there is usually very little actual physical contact.

It is best to observe but not intervene during these squabbles to enable them to establish the hierarchy between them unless there is prolonged physical fighting or injury in which case they may need to be housed separately. Occasionally a very dominant hamster may not accept living with another but this is rare.

Its probably domination, they both think that theyre the boss of eachother and are fighting to prove it.