In the present study Blood was collected from dogs (n=110) after clinical examinations and recording of necessary information(age, sex, breed and housing)
examined by modified knott method. Periodicity of the microfilaria in peripheral blood circulation, was determined through blood collection from a dog each hour
for 72 hours. Number of microfilaria in each ml of the blood samples was calculated and expressed as average of microfilaria in each hour. Results showed that 15.45% of dogs were infected by Dirofilaria immitis and 4.55% by Dipetalonema reconditum. Statistical analysis did not show significant relationship between infection and age,sex, breed and housing status. Furthermore, maximum and minimum numbers of microfilana were seen at 1 am(13316 microfilaria) 12 am(6681 microfilaria) respectively.Therefore, by considering the infection of dogs on Golestan province and its transmition to other animals,control of above-mentioned nematode should be done by treatment of infected dogs and eradicution of stray dogs.