Abstract: Dynamics of standing crop of N and P for fine roots of pure and mixed Tsoongiodendron odorum forests of Cunninghamia lanceolata were studied. The standing crop of N and P for fine roots of mixed forest were 1.3 and 1.2 times, and annual return were 1.23 and 1.14 times as much as those of pure forest, respectively, which were 38.3% and 67.4% of those returned through litterfall. Annual decomposition was 1.26 and 1.23 times, and annual accumulation was 1.23 and 1.14 times, respectively, as much as those of pure forest. It showed that fine roots of mixed forest had a higher accumulation capacity and a more rapid turnover rate of nutrients. Fine roots of undergrowth played an important role in nutrient cycling of fine roots of forest community. Roots 0.5 mm in diameter was the major body in nutrient cycling of fine roots. Seasonal dynamics of standing crop of nutrient in living fine roots of C. lanceolata showed a single apex curve for N and double apices one for P, and those for N and P in dead fine roots both showed an "S" curve. The dynamics for fine roots of T. odorum were similar to those of C. lanceolata, except for that of P in living roots which showed a single apex curve. The dynamics of standing crop of N and P for living fine roots of undergrowth in both stands showed a double apices curve, and those for dead roots showed a single vale one.