Really the issue should have been decided in the divorce agreement so as not to have to deal with it later on.  But what is done is done.  Be aware, though, that the court could still rely on the law as it relates to interspousal gifts to decide the issue. It is my understanding that gifts given during the marriage are generally considered to be separate property in Mississippi.  Your ex probably has the bill of sale for the dog and that is why he had the info changed on the chip.But the bill of sale does not mean that it was not a gift.  He is going to try and take you to court regardless and you should be prepared to prove your defense: gift given during marriage.  Witnesses to the event, a birthday card indicating the dog was a gift - whatever.  Good luck.