Abstract: The epidemiological characteristics of leptospirosis reported in Yichang area during last 20 years were vestigated. The results showed that this disease occurred periodically wlth a cycle of 10 years. The factors for the periodic occurrence were related to the decrease in the herd immunity level of the population the increase in carrier rate in rodents. In most cases, the disease was of influenza-typhoid type, and presented some difficulties in diagaosis and resulted in some epidemic districts unknown to the health authorities for a long time.