[Aim] The cassava green mite, Mononychellus mcgregori is a newly established pest on cassava in China. The species also lives on rubber tree (Hevea brasiliensis) and threatens the rubber industry. Recently, M. mcgregori was recorded in cassava-planting areas in Hainan, Yunnan, Guangxi and Guangdong Provinces, where it caused significant damage, reducing the fresh root yield of cassava by 40%-60%. Humidity is an important ecological factor for the development and the reproduction of M. mcgregori but precise information about the effect of various humidity conditions is lacking.[Method] Effects of humidity on the development and reproduction of M. mcgregori were studied under laboratory conditions.[Result] When the relative humidity (RH) was 75% and 85%, both of the hatching rate was 100%, mean fecundity per female was 49.22 and 43.67, respectively, longevity of female adults was 21.00 and 22.00 d. The hatching rate, fecundity and longevity of female adults significantly decreased at 55% and 95% RH. The developmental duration at 65% RH was significantly prolonged but the hatching rate, fecundity and longevity of female adults were not significantly different between 65% RH and 75%-85% RH.[Conclusion] The most suitable humidity range is 75% and 85% for the development and reproduction of M. mcgregori.