DIROFILARIA IMMITIS, which is otherwise known as heartworm, is an important parasite in dogs and other carnivores. It lives in the right ventricle of the heart, the pulmonary artery and the posterior vena cava, and its microfilaria can be found in the peripheral circulation. This is the first report of DIROFILARIA IMMITIS Infection in STRAY DOGS in KHUZESTAN, a province in South-Western IRAN. Blood samples from 119 STRAY DOGS were collected randomly from different districts of KHUZESTAN. The samples were examined by the modified Knott's method. Blood microfilaria of DIROFILARIA IMMITIS were observed in 15 samples (12.61%). The most severe infections were seen in 7-yr-old male dogs and also those in the Dezfool district. However, statistical analysis by the Chi-square method did not show a significant relationship between the rate of infection and other factors, which included age, sex and geographical distribution. As this parasite can infect humans, the infection of dogs with D. immitis in KHUZESTAN should be controlled by the removal of the dogs and the vectors of D. immitis are insects including flies.