BACKGROUND: Over the recent years, Neospora caninum has been one of the most important causes of abortion in dairy cattle. OBJECTIVES: We conducted the present study in order to investigate the seroprevalence of N. caninum in dairy cattle in Semnan province and its effect on abortion. METHODS: 237 blood samples were obtained from various Semnan dairy farms and 104 bulk dairy samples from four milk collection centers in Semnan, Garmsar, Damghan, and Shahrood were tested for sera and milk utilizing ELISA (Svanova Biotech AB) test kits. RESULTS: The results revealed that 87.27 % of bovine serum was positive. The percentage of opacity density (OD) of positive sample (PP) ranged from 72.17 to 137.3 (114.21±24.65). In addition, the average rate of milk seroprevalence to the parasite was 95.23 % in Semnan province. CONCLUSIONS: The frequency of Neospora caninum infection in blood and milk was high in Semnan, yet no significant relationships were observed with abortion (p < /em>>0.05).