In order to study the effect of Laccaria bicolor on the growth and root morphology of Pinus thunbergii seedlings, we inoculated the seedlings of P. thunbergii with liquid fungus of L. bicolor in nutrition cup. We compared the differences of biomass, root morphology and root fractal dimension between inoculated and uninoculated P. thunbergii seedlings. The results showed that the L. bicolor showed obvious promotion effect on growth and biomass accumulation of underground roots and aboveground plants of P. thunbergii seedlings. Inoculation of L. bicolor also significantly improved the total root length, forks, root surface area, root volume and root fractal dimension. Moreover, its promoting effect on the growth of underground roots was earlier than that of the aboveground part, and the effect was significantly higher than that of the aboveground part. 15-30 days after the inoculation, L. bicolor had no effect on the aboveground part, but it had obvious promotion effect on the root system. However, the aboveground part began to show significant growth response on the 60th day. In summary, the L. bicolor can colonize the root of P. thunbergii successfully, promote the growth of seedlings and the accumulation of biomass, increase the total length, forks, surface area and volume of root system, and increase the fractal dimension of root system. It showed obvious promoting effect on root development, and the promoting effect was earlier befor the aboveground part growth.