Abstract: The effects of the activity of alkaline phosphatase in intraradical hyphae of three arbuscular mycorrhizae fungi on the growth of maize arc'studied in this paper．The results shaw that G．m and G．i inoculated treatments can significantly improve the dry weight of the maize plants，P concentration and P uptake by maize plants compared with G．spp inoculated treatment But there is no significant difh rence bctween G．m and G．i treatments At 35 days after sowing (DAS)，alkaline phosphatase(ALP)actix，ity in intraradical hyphae of G．m and G．i is significantly higher than that of G．spp．howexer no significant difference appears between G.m and G．i .The changes of alkaline phosphatase activity of G．m and G.i at the infection age show similar trends．Alkaline phosphatase activity is highest at 35 DAS，but decreases sharply from 35 to 50 DAS and then keeps stable up to 70 DAS．As far as G．spp concerned．there is a little fluctuation of alkaline phosphatase activity at infeetion age，and the enzyme activity always keeps very low．In other words，when inoculatlng arhuscular mycorrhizae fungi with high alkaline phosphataes activity(35 DAS)，the maize has a great improvement of dry weight and P nutrition．Otherwise，there is no significant effect when the maize is inoculated with arbuscularmycorrhizal fungi of low alkaline phosphatase actixrity．In conclusion，ALP activity in intraradical hyphae at 35 DAS is a useful physiology marker for predicting AM fungi effect on mycorrhizal plants．