The biologically active peptidoglycan was purified form the alkali fraction of the fruiting bodies of Ganoderma lucidum and the composition of the peptidoglycan was investigated by conventional analyses. The alkali-extracted peptidoglycan showed differences in chemical compositions from the water-extracted. The alkali-extracted peptidoglycan contained 6.9% protein and 75.9% carbohydrates composed mainly of $eta$-glucose, mannose, and $alpha$-glucose. The molecular weight range of the peptidoglycan was determined as 2,000 kDa-17 kDa. The peptidoglycan is considered to be a hybrid molecule of polysaccaride chains covalently bound as a side chain to the polypeptide core.