Abstract: One of the real problems that cause the public health risks in small animal yearly is parasitic diseases and some of these parasites are zoonoses. To overcome these problems, the use of antiparasitic drugs is necessary. Ivermectin is a broad spectrum antiparasitic agent and different routes of its administration such as injection, oral and pour-on were used. The aims of the current study were evaluation of the efficacy of ivermectin pour-on administration against natural Dirofilaria immitis infection in native dog and also determination the prevalence rate of this parasite in East-Azerbaijan province, Iran. In the present study, 60 native dogs were investigated by detection and enumeration of circulating microfilariae of Dirofilaria immitis were carried out at each visit by the modified Knott test. After confirming the infection with worms, ivermectin (0.5 mg kg^-1) pour-on was administrated to infected dogs. Blood examination was repeated in 1, 7, 21 and 28 days post treatment. Results showed that total prevalence of Dirofilaria immitis infection was 71.66% in native dog of East-Azerbaijan province, Iran. Efficacy rate of ivermectin pour-on was 31.42, 63.49, 88.66 and 98.54% in 1, 7, 21 and 28 days, respectively. In conclusion, the effect of this drug against Dirofilaria immitis resulted in reduction in Knott test exceeded 98% so, this drug can be used in antiparasitic program in dog. Further investigations are necessary to evaluate the drug effect on other nematodes and parasitic infections.