Abstract: Based on our previous studies on the physiobiochemical characteristics of allelopathic rice.GC-MS and biochemical analysis were introduced to determine allelochemicals and its related enzyme activities. It indicated that the activities of phenylalanine aminotransferase(PAL) and trans-cinnamic acid-4-hydroxylase (CA4H) in allelopathic rice were positively correlated with the content of phenolics.The rice allelopathic effect was positively correlated with its content of cinnamic acid, but negatively correlated with its content of salicylic acid.Therefore it was considered that rice allelopathic effects were caused by the joint action of phenolics.