This study investigated the prevalence of Cryptosporidium in stray dogs in Tabriz city, Iran, and evaluated the efficacy of a combination of Clindamycin and Trimethoperim/ Sulfadiazin for treating Cryptosporidiosis. Faecal samples of 200 stray dogs were examined by Ziehl Neelsen microscopic method and the results showed that 12 (%6) collars showed infection with Cryptosporidium, with 8 collars in female and 4 in male dogs. According to the age of the dogs, 9 dogs under one year (Puppy) and 3 adult dogs over one year old (%1.5) were diagnosed with Cryptosporidium. There was a statistically significant difference in the prevalence of Cryptosporidium between male and female dogs (p<0.05). A treatment course of clindamycin (25 mg/kg/day) and trimethoprim/sulfadiazine (15 mg/kg PO bid for 7 days) was administered and 10 dogs (%83.4) were cured, while 2 dogs showed positive cases. The results suggest that a combination of Clindamycin and Trimethoperim/Sulfadiazin is an effective treatment for Cryptosporidiosis in dogs, but further studies are needed to provide precise pharmacological explanations.