Instructions
Arrange a meeting between your Chihuahua and a family member's or friend's dog. The dog that your Chihuahua will be meeting should already be socialized and have a good track record for getting along with all types of dogs. Make sure that your Chihuahua isn't hungry or in need of relieving himself before the meeting. Also, don't excite your Chihuahua beforehand with play or exercise.
Place a leash on your Chihuahua before he sees the other dog. Introduce the dogs and let them smell and explore each other.
Pull back on your Chihuahua's leash at the first sign of aggression and command them "no." Keep the leash taut so that they can't run around or jump. If your dog continues to be aggressive, command them to "sit." If the aggression doesn't stop, take several steps back from the other dog or bring your Chihuahua into a separate room. Try to let the dogs meet each other again once your Chihuahua has calmed down.
Reward both dogs when they are able to be around each other without acting aggressively. Even if the other dog is always well-behaved, be sure to offer both the other dog and your Chihuahua treats so that you don't breed resentment.
My Chihuahua Won't Play With Other Dogs
Even the smallest dogs can show signs of aggression. Every dog has a different, unique personality, so while you may have one Chihuahua that plays well with other dogs, you could have another that is constantly territorial. Signs of aggression can including barking, nipping, biting or preparing for a fight. When any dog feels that their space is being threatened, they become scared and act out. It is possible, though, to train your Chihuahua to tolerate other dogs and possibly even get along with them.