The objective of this study was to increase the intracellular polysaccharide yield of Ganoderma lucidum. The accordingly optimized fermentation medium by central composite design method contains glucose 40 g L-1, yeast powder 12 g L-1, potassium dihydrogen phosphate 3 g L-1, initial pH 5.5, and inoculum size 10 mL 100 mL(-1). Under this condition, the predicted value of intracellular polysaccharide yield was 2.03 g L-1. Shake flask experiments confirmed that the average intracellular polysaccharide yield was 1.98 g L-1 similar to the predicted value. The yields of intracellular polysaccharides in the 5-L and 50-L fermentors were 2.59 g L-1 and 2.65 g L-1, respectively. The molecular weight distribution of intracellular and extracellular polysaccharides obtained was determined by HPSEC-MALLS-RI. The results showed that the weight-average molecular weight of component 1 in the intracellular crude polysaccharide was 4.695 x 10(6) Da and the mass fraction was 58%. The weight-average molecular weight of component 2 in the extracellular polysaccharide was 5.554 x 10(4) Da. The mass fraction was 94.9%. The liquid submerged fermentation process of G. lucidum mycelium obtained from this study has effectively increased the yield of intracellular polysaccharides. Its intracellular and extracellular polysaccharides have good immunological activity. Conceivably, the optimized process can be applied for the large-scale production.