Abstract:In this study， the single-factor method and orthogonal design were used to optimize the flask culture conditions for exopolysaccharide （EPS） production by Phellinus vaninii Ljup. The morphological changes in optimal medium mycelia were also investigated. The results of single -factor experiment for EPS production showed the optimum growth cycle 8 days. And the best carbon source， nitrogen source and inorganic salts were sucrose， corn steep powder and KH2PO4， the optimal temperature of 28 ℃， pH 7. Then， the concentrations of three factors， i.e. carbon source， nitrogen source and inorganic salts was optimized using the orthogonal design and the optimum culture medium for EPS production were 40 g/L sucrose， 4 g/L corn steep powder， 4 mmol/L KH2PO4. Under the optimial culture conditions， EPS yield was 0.352 g/L. The morphology under the optimal medium was invesitaged during the fermentation period. The mycelial pellets increased gradually， and the average diameter and density also increased， but roundness increased first then decreases sharply. The roughness first decreased and then increased， which was negatively correlated with roundness.