To extend the shelf lives of rice and corn products, the effects of the polyphosphates[$Na(PO_3)n$, n=11] on the growth of Penicillium griseofulvum and patulin production were investigated. The growth was completely inhibited in the potatoes dextrose agar medium treated with 2% polyphosphate. Moisture content had a considerable influence on the production of patulin. At 30% moisture content, the amounts of patulin produced in rice and corn were $61.40 mu g/ml$ and $40.74 mu g/ml$, respectively, but the level of the toxin was significantly decreased to 93~95% by addition of 1% polyphosphates. No patulin was detected in both rice and corn medium added 2% polyphosphate when the incubation time prolonged. The result of scanning electron microscopy was supposed that the biocidal action of polyphosphate on fungi was related to the collapse of cell wall structure.