Abstract: Schistosomiasis prevails in 17 counties and cities in Yunnan Province.Approximately, a population of 301 511 were affected and the snail-ridden area amounted to 219 000 000m2 in the past years. These endemic areas were not evenly distributed, but rather scattered.The endemic foci were vertically distributed at an altitude of 1 350-2 450 metres above sea level. Human cases were found mostly in areas with an elevation of ≥1 800 metres, and became progressively fewer with the ascent. However, in areas with an-elevation of ≤1800 metres, the infection rate in the inhabitants decreased with the descent.In areas with an average temperature of 11.8-19.5℃ and the annual rainfall up to 574-970mm, transmission of the Schistosomiasis was always present, suggesting an annual mean temperature around 15.7℃ and rainfall 800-900mm were favourable factors for Schistosomiasis transmission.The cultivated areas with paddy soils were most suitable for the breeding of Oncome-lania snails, where Schistosomiasis was severely prevalent. Only a few Oncomelania snails and patients were observed in areas covered with red loam. No patient or snail was found in areas with brown loam or mountain meadow soil.