The fate of C and N was monitored in a clay-textured soil (Typic Haplocambid) which was either unamended (control) or amended with various plant materials at the rate of 10 g residue C/kg soil. To evaluate C mineralization, soils were incubated for 46 days under aerobic conditions. Nitrogen mineralization/immobilization was evaluated at the end of eight-week incubation experiment. All CO2 evolution data conformed well to a first-order kinetic model. The product of K and Co (KCo) was significantly correlated with some chemical and biochemical properties of the plant residues, including N concentration (r=0.83, P less than 0.001), C:N (r=-0.64, P less than 0.05) and lignin:N (r=-0.81, P less than 0.001). Among the plant residue composition characteristics, N concentration (r=0.96, P less than 0.001), C:N (r=-0.69, P less than 0.01) and lignin:N (r=-0.68, P less than 0.01) were significantly correlated with the net rates of N mineralization/immobilization.