Abstract: In order to investigate the effects of dietary l-arginine addition on semen quality, genital ultrasound parameters and serum testosterone in male dogs, in the experiment, a police dog base in Shenyang City selected 20 healthy male Spaniels aged 4-5 years with similar body weights, and they were randomly divided into four groups（n=5）, namely, test group A, test group B, test group C and the control group. Groups A, B and C were supplemented with 10, 15 and 20 mg/kg l-arginine per day per body weight, respectively, and the control group was not supplemented with l-arginine; the experimental period was 30 d. Semen quality（semen volume, semen, density spermatozoa, and viable spermatozoa viability）, genital ultrasound parameters（testicular width, testicular depth, and epididymal caudal thickness）, and the mass concentration of serum testosterone were examined in each group on the 1st, 10th, 20th, and 30th days of the test. The results showed that on the 1st and 10th day of the experiment, the differences between the groups in each index were not significant（P＞0.05）. On the 20th day of the test, semen density and sperm viability of test group A, test group B and test group C were significantly higher than those of the control group（P＜0.05）, and semen density of test group B was significantly higher than those of test group A and test group C（P＜0.05）; and testicular width and testicular depth of testes in the left and right sides of test group B and test group C were significantly higher than those of the control group and test group A（P＜0.05）. On the 30th day of the test, semen density and sperm viability of test group A, test group B and test group C were significantly higher than those of the control group（P＜0.05）; semen density and sperm viability of test group B were significantly higher than those of test group A and test group C（P＜0.05）; semen density of test group C was significantly higher than that of test group A（P＜0.05）; the testicular width, testicular depth and caudal thickness of epididymis of the left and right sides of the testes in test group B and test group C were significantly higher than those of the control group and test group A（P＜0.05）; the serum testosterone mass concentration of test group B and test group C was significantly higher than that of the control group and the test group A（P＜0.05）. The results suggested that the addition of l-arginine to the diets could improve the semen quality, genital ultrasound parameters and serum testosterone mass concentration of male dogs; the best effect was achieved by the addition of 15 mg/kg l-arginine per day according to body weight under the conditions of this experiment.