We studied the effects of several medicinal insects on biosynthesis of polysaccharides from Ganoderma lucidum in submerged culture. The results showed that the medicinal insect, Catharsius molossus at 5 g/L significantly promoted the biosynthesis of intracellular polysaccharides (IPS) and extracellular polysaccharides (EPS) of G. lucidum, and compared with control, IPS and EPS yields markedly enhanced from (1.93 ± 0.09) g/L to (2.41 ± 0.12) g/L and (520.3 ± 20.2) mg/L to (608.9 ± 20.2) mg/L, respectively (P < 0.05). Both IPS and EPS consisted of five kinds of components, and IPS-1 and EPS-1 were the major components of IPS and EPS, respectively. Further separation studies showed that IPS-1 was made up of three single compounds, while EPS-1 was made up of two single compounds. There were no new components in both IPS and EPS obtained from G. lucidum in submerged culture by the addition of the insect, C. molossus, suggesting the biosynthetic pathways of the major components of IPS and EPS had not been changed.