Previous report showed that watermelon consumption has an anti-obesity effects in rats. The purpose of this study is to examine the effects on body weight, body fat percentage, serum biochemical data, serum adipokine concentrations (leptin, adiponectin, and resistin), urine specific gravity and sediments when 12 dogs were given watermelon extract beverage instead of water for 3 months. Those data were all assessed before the study period and again at 1.5 and 3 months. Although there were no remarkable changes in most of these parameters, a significant decrease in serum leptin concentrations at 1.5 and 3 months. Calcium oxalate and struvite crystals were observed in the urinary sediment in five dogs; although their urine specific gravities remained >1.040 throughout, the number of urinary... crystals had decreased by the end of the 3-month period. Morphological components were not found in the urinary sediment of the other five dogs; their urine specific gravities were also >1.040 before the study period and at 1.5 months, but these had decreased to <1.040 at 3 months. These results suggested that drinking the watermelon extract beverage reduced serum leptin levels and inhibited the formation of urine crystals such as calcium oxalate and struvite crystals in dogs.