Abstract: Five fungi species including Rhizoctonia sp.,Sclerotium sp., Acremoniell sp., Chaetomium sp.and Pestalo-tiopsis sp.screened from the inner bark of Sapium sebiferum (Level) Roxb.were used to study their growth under different environmental factors, with the biomass and fatty acid composition as main indexes to elucidate the relationship between plant and its endophytic fungi.Compared with that from synthesized medium, a higher biomass was harvested when the fungi were cultured on liquid potato dextrose medium; the unsaturation index of fatty acid (IUFA) was lower, and the main fatty acids in the fungi were linoleic acid, palmitic acid and oleic acid.Compared with the fungi grown on the synthesized medium without Sapium sebiferum' s extract, the Sclerotium sp.growth was promoted, and the others were inhibited when the extract was added to the synthesized medium.At the same time, the IUFA were increased.When0～1.0 mol·L^-1 NaCl was added in Sclerotium sp.'s culture medium, the biomass was not changed notably; IUFA in 0～0.5 mol·L^-1 NaCl was not significantly different, while in the range of 0.6～1.0 mol·L^-1 NaCl, the IUFA was decreased with increasing concentration of NaCl.It indicated that fungus had a stronger tolerance to salt.Sclerotium sp.'s growth was promoted, and the IUFA was increased when plant oil was added in the synthesized medium.The biomass was the highest by adding1.5% plant oil.The results mentioned above were some way related to the symbiotic relations between the endophytic fungi and their host plant.