Background: Leptospirosis is the most common zoonosis widespread in tropical and temperate countries with low social-economic status. We aimed to compare an ELISA kit with an in-house ELISA assay to test the serum samples of the patients who were suspicious of leptospirosis according to their clinical symptoms. Methods: A total of 282 serum samples of patients suspicious of leptospirosis admitted to hospitals in Rasht city (north of Iran) were examined for sero-diagnosis of leptospirosis. Blood samples were obtained with mean time of 6.36 days after the onset of the symptoms. Antibodies were detected using a commercial qualitative and by an in-house semi quantitative IgM and IgG ELISA and the results were compared with microscopic agglutination test (MAT) as the gold standard. All specimens with titers ≥320 against a pathogenic serovar in MAT were considered positive for leptospirosis. Results: The results of MAT have demonstrated that 70 serum samples (24.8%) had a positive reaction with one of the leptospira serovar. The sensitivity, specificity, positive and negative predictive values were 87.1% , 91.0 %, 67.8%, and 95.5% for in-house ELISA assay, respectively, and 100%, 42.9%, 36.6%, and 100 % for commercial IgM ELISA assay, respectively. Conclusion: Our results showed that IgM ELISA assay is a reliable and sensitive method for the laboratory diagnosis of acute leptospirosis. In-house semi quantitative IgM ELISA was more specific and commercial IgM ELISA was more sensitive.