Melanoma consider the most common tumor that affect about 80% of Arabian horses. Gray color of Arabian horses is the most susceptible to melanoma than other colors that make many researches confirm that there are link between graying color mutation and melanoma. Melanoma is a hereditary disease that affect horse life, performance and appearance so study this disease is very important to recognize causes of this disease and determine best treatment. In this review we will discuss severity of melanoma on horses, distribution, histopathology, differential diagnosis of melanoma, link between gray color and melanoma occurrence and genetic background of melanoma