my dog's poor eating habit

What are you feeding him? It could be that he just doesn't like his food. It could also be medical issues like those mamasan34 writes about but the first thing I'd try is different kinds of foods (high quality ones, not superstore market junk brands like pedigree). If you've already done that, then I think another trip to the vet would be in order for some thorough examinations and testing.

If your vet has examined him and hasn't found any reason for his poor eating habits, you might be interested in reading this article about getting finicky dogs to eat. http://www.associatedcontent.com/article/270251/feeding_a_finicky_fido_how_to_get_a.html. Hope it helps.

You didn't say how old your dog was or if he suffers from any medical issues. If he is older, there are many reasons why a dog could lose his appetite. These are some explanations I pulled off of the Pedigree site: Dental pain. If your dog is experiencing pain from a fractured tooth or gum disease, chewing can be very painful. Loss of smell. Older dogs don’t have as sharp a sense of smell as they had when they were younger. Because of this, their food may seem less appealing. You can remedy this by adding canned food or gravy to the food. Intestinal problems. Worms, viruses that attack the intestines, ulcers, food allergies, and certain cancers can create digestive discomfort or nausea, preventing your dog from eating. Liver disease. If a dog’s liver isn’t functioning properly, the brain will be affected which, in turn, will decrease his appetite. Kidney disease. Mouth and stomach may cause both loss of appetite and discomfort. You may also notice an increase the consumption of water. In my experience sometimes a dog just gets tired of his regular food and needs a change. Maybe throw something different in like some gravy or some soft dog food mixed in. Just some suggestions.