Background and purpose: Hydatidosis is one of the most important zoonoses in the world that have public health and economic perspectives. The aim of this study was to investigate the prevalence of hydatid cysts in slaughtered animals in the industrial slaughterhouse of Khomein, Markazi province (2007-2011(. Materials & Methods: In this study was invistigated 28760 head of animals, including 12860 sheep, 3840 cows and 12060 goats. Their carcasses were inspected using macroscopic method for hydatid cyst in livers and lungs. Data analysis was performed by Chi-square test and SPSS software (Version 16.0). Resuts: The prevalence frequency of hydatidosis in slaughtered cattle was 523 head with the most infected animals of 113(2.94%) cow, 223(1.73%) sheep and 187 (1.55%) goats respectively. Moreover, 1126(3.9%) infected lungs and 1076(3074%) infected livers were found. On the seasonal bases, the surveys showed that maximum spread of the disease was in summer. Conclusion:The prevalence of hydatid cysts of parasites is relatively high which in addition to imposing high economic losses due to the deleting of infested organs of animals and decrease in livestock products, indicates the existence of conditions for health risks for residents which requires more inclusive and comprehensive sanitary and control measures due to this parasite's life cycle and transmission.