Background & Aims: Hydatidosis as a parasitic zoonotic infection is endemic in Iran, but systematic information about the exact rate of hydatidosis prevalence in different regions of the country is very limited. Because of the importance of disease this study was undertaken in East-azarbaijan province to determine the prevalence rate of hydatidosis by ELISA method. Methods: Totally, 1500 serum samples were collected from patients referred to different health centers in 8 cities of East-Azarbaijan province in 2009. Antigen B was obtained from infected sheep’s lung and liver. All sera were checked in 1:400 dilution by ELISA test. Optimal antigen concentration and serum dilution were determined by cross-titration method. Data were analyzed with t-test and chi-square. Results: Overall, 19 cases (1.28%) were positive for human hydatidosis, of whom 8 cases (0.93%) were from urban population and 11 cases (1.8%) were from rural areas. There was no significant difference between urban and rural population in this regard. Also 1.76% of females and 0.83% of males were positive that shows significant difference between two sexes (P<0.001). Age group of 30-40 years old had significantly (P<0.001) the highest rate of positive cases (1.66%). Conclusion: According to the results of this study, in East Azarbaijan hydatidosis is an important endemic disease with a considerable prevalence. Because of high rate of infection in different age and occupational groups, prevention and control of this disease should be considered as one of the health priorities. Moreover, further studies are needed to investigate the sources and transmission routes of the infection.