Abstract: Cheyletus malaccensis(Oudemans) is a kind of predatory mite,which widely exists in grain storage warehouses,and is a potential natural enemy for stored-product pests.Based on the usual temperature and relative humidity condition of pest occurrence in granary,the growth and development of C.malaccensis were studied at 24℃ with different relative humidity (RH(65±2)%,(75±2)%,(85±2)% and (95±2)%),fed with Acarus siro (Linnaeus),and this study will be helpful for using C.malaccensis to control stored grain pest and its artificial reproduction in large-scale.The results showed that C.malaccensis experienced five stages,including eggs,larvae,protonymph,deutonymph and adult,deutonymph was absent in males'development.At RH(85±2)%,the time from egg to adult was the shortest with an average of 16.3 days,and the longest development time was RH(65±2)% with an average of 18.6 days.The male mites in the RH(95±2)% had the shortest development time with an average of 12.6 days,and the longest development time with an average of 14.7 days at RH(65±2)%.At RH(65 ±2)%,the adult stage and the total development period were the longest,83.5 and 95.8 days,respectively.Humidity significantly affected on the adult stage and the development duration of all stages.The maximum average number of eggs per female,oviposition period and daily fecundity were 493.0,46.2 days,10.3 respectively at RH(85±2)%.This study provides basic biological parameters for C.malaccensis to control stored grain pests and mite.