Serendipita indica (formerly known as Pirifor-mospora indica), a root endophytic fungus, exhibits mul-tiple functions in some agricultural, horticultural, and medicinal plant species. We studied colonization of the roots of Platycladus orientalis, a forest tree species, by S. indica to improve the quality of the seedlings in seedbeds and survival rates in sylviculture. At 20 days after inocu-lation, S. indica colonized the root cortex of P. orientalis seedlings. Root colonization by S. indica significantly increased net CO2 assimilation, light use efficiency, and biomass accumulation by both roots and shoots, whereas it did not affect the biomass allocation between roots and shoots. In addition, the symbiosis significantly increased root total length, surface area, and volume. In view of the two specific traits of S. indica, i.e., axenic culture and wide colonization in plants, the fungus might be used for improving quality of P. orientalis seedlings and increasing their survival after transplanting.