The enzyme activities of straws, animal manures, composts and other organic materials widely used in Huang-Huai-Hai region were studied. Among all tested materials, straws showed stronger activities of invenase and amylase than other organic manures. Except some cases, urease and protease activities in animal manures were stronger than those in other organic manures. Soybean straw was proved to be the best one with enzyme activities, but sludge was worse than other organic manures. Under laboratory conditions, straws and animal manures could strengthen the activities of invertase, phosphatase and urease in fhtvo-aquic soil to varying degree. Field test showed that urease and phophatase activities, in soil applied with more wheat straws were stronger and those in soil applied with less ones were weaker. Organic manures not only strengthened enzyme activities, but also had great effects oa soil N and P transfomations.