Moulds have been a long standing hazardous problem in food industry because it produces harmful mycotoxins. How to control moulds in the processing of tea has been a difficult technical problem for a long time. This work studied the mould preventing effect of microwave treatment on tea products and their controlling conditions. It was shown that the microwave sterilizing treatment grew more effective with the increased moisture of the tea. And the effect is also related to the quantity of tea treated, the material of container and the diffusion of water. An 800?W microwave oven killed all the moulds in 250?g tea within 135 seconds and in 250?g fresh or fermented tea within 120 seconds. Conversely, slight microwave heating augmented the growth of moulds in tea. A microwave treatment over 150 seconds harmed the quality of the tea. It was concluded that microwave treatment in the preliminary processing of tea can effectively control the growth of moulds, and at the same time dry the products. The conditions in which moulds are under control in the processing of tea with microwave are also discussed here.