Background and objectives: Rheumatic fever is a main problem of developing countries, whereas in developed countries its prevalence is low. Proper diagnosis and adequate treatment of beta streptococcal infection can effectively prevent such unwanted sequel. Materials and Methods: Following completion of a questionnaire regarding age, sex, location etc. blood sample was collected and ASO titer was measured. Results: Out of 400 samples, 54 patients had positive ASO titer. 83.3% of individuals with a positive titer had the history of pharyngitis. Positive ASO titers in rural and urban area were 19% and 11.6% respectively. Positive ASO titer in females and males were 68.5% and 31.5% respectively. Age distribution of positive titer was 42.6% in 20-29 years age group and 37% in 10-19 years age groups. Conclusion: patients with positive ASO titer in Zanjan province and surrounding villages were relatively high which might be due to low education level and poor economical status. The incidence was high in the second and the third decade of life whereas in other countries this range is between 6-15 years. High incidence of rheumatic fever in the studying population seeks a prompt measure to be taken on the prevention and control of streptococcal infection.