Introduction:In Vietnam,local commercial rice has been badly stored,and it has been sold without packing,it is directly exposed to the moist warm air.Clearly,the rice will absorb water vapour and the moisture content will consequently increase.Under such conditions,mould may multiply and possibly produce mycotoxins.Their presence in rice is of considerably concem to the consumers health since rice is the staple diet.So the effect of the relative humidity of the air on the aflatoxin B1 (AFB1) production of Aspergillus parasiticus was examined in this study.