In natural reserve of Jianou, Fujian, fine roots of Castanopsis carlesii and Cunninghamia lanceolata were selected and categorized into 0-1mm and 1-2mm size classes in diameter to study their mass loss and nutrient release in decomposition by litterbag experiment with mono-specific and mixed litter in both C. carlesii and C. lanceolata stands for 720 d. At the initial phase (0-270 d) of decomposition, a synergistic effect of root mixtures on the mass loss was observed. However, an antagonistic effect dominated at the late phase (270-720 d) of decomposition. The pattern of nutrient release differed from that of mass loss in the decomposition. In the initial phase (0-360 d) of mixed decomposition, a synergistic effect was shown for the release of N, P and K, while an antagonistic effect for the release of N, K in the later phase (360-720 d) except for P which showed a neutral effect. The effect of fineroot mixture on mass loss and nutrient release could be closely related with the dynamics of soil decomposer community, which necessitates the further investigation.