Why does my dog always cough?

You'll need to take your dog to a vet for a diagnosis, as may things can cause coughing in dogs. A few possibilities: kennel cough, respiratory infection, collapsing trachea, heart disease, pneumonia, heartworms, etc.

You may want to jot down what the dog has been doing just before he coughs as it may help your vet to determine the cause. Hope it's nothing serious!

let me answer this question with another question. Do you walk him and what sort of collar does he wear when he's being walked? Small dogs have very weak tracheas and he could be choking. Do use a halter. 2nd, I've had my small dog for 3 years now and he often "clears his throat" and it is no big deal. Really think your dog is fine.