This study was conducted on 210 dairy cows in Mianeh area in Iran in order to determine seroprevalence of leptospiral infection. Sera were initially screened at dilution of 1:100 against 7 live serovars of Leptospira interrogans: Pomona, Canicola, Hardjo, Ballom, Icterohaemorrhagiae, Automenalis and Grippotyphosa using the microscopic agglutination test. The prevalence of leptospiral infection (At titers 100 and 200) was 7.14% in dairy cows. There was significant relationship between aging and the incidence of leptospiral infection (P<0.05) and There was no significant relationship between breed of the dairy cows and the incidence of leptospiral infection. The highest number of reactors in dairy cows (40%) were due to serovar Pomona and serovar Icterohaemorrhagiae, followed in descending order by Grippothyphosa (20%). All off the sera were seronegatives for Hardjo, Canicola, Ballum and Autominalise. The majority of titre levels were between 100 and 200 for all the serovars. These results confirm that the majority of leptospiral infections is asymptomatic and the presence of antibodies in the absence of infection indicates exposure to the organism in these animals.