Field experiments were conducted to study dynamics of soil microbial biomass N (MBN) and soil enzyme activities including urease, dehydrogenase, catalase and protease activities, and correlations with soil nutrients and N uptake of rice in rice-duck and rice-fish ecosystems from May to September in 2007. The experiment field was averagely divided into nine plots for three different treatments, and the three experimental treatments were (1) conventional rice field (CK), (2) rice-duck ecosystem (RD) and (3) rice-fish ecosystem (RF). The results showed that RD and RF could enhance soil MBN content and urease, dehydrogenase and protease activity but not affected catalase activity. During rice growth, soil MBN content increased firstly after transplantation, and subsequently decreased and slightly increased at rice autumn. The soil enzymes activities ascended at the early stage and then declined slightly except that catalase activity slightly changed. Linear regression analysis showed that no close correlations existed between soil MBN and soil enzymes activities, soil nutrients (available N (NH+4 + NO-3), total N and total P) and N uptake of rice, and between soil enzymes activities and soil total N and total P. Moreover, Soil urease and dehydrogenase activities were closely related to soil available N, and N uptake of rice was closely related to soil urease, dehydrogenase and protease activities.