Aim: The purpose of this study was to investigate the clinical efficacy of gamithromycin in the treatment of naturally infected neonatal calves with cryptosporidiosis. Materials and Methods: 5-20 days old 20 diarrheic neonatal calves were used as material in this study. Diagnosis of cryptosporidiosis was made by microscopic examination and ELISA test. Calves shedding Cryptosporidium oocysts between 4 x 104 and 15 x 106 per gram in feces were included in the study. Hemogram and blood gases were measured at the beginning of the treatment and after the treatment. A single dose of 6 mg/kg body weight of gamithromycin was administered subcutaneously. Drug efficacy was assessed by evaluating the existence of diarrhea, oocyst shedding and body condition from day 1 to 5. Results: On 5th day, the medicated 6 calves had no oocysts, and number of oocysts in feces had been decreased in 11 calves on 5th day. Statistically significant difference (p<0.05) was observed in the blood values at the beginning of the treatment and after the treatment. Conclusion: It has been determined that based on both clinical improvement and decrease in oocyst count in feces, gamithromycin was found to have moderate effect in the treatment of cryptosporidiosis in naturally infected neonatal calves.