By investigating the shear effect on submerged cultivation of a traditional Chinese medicinal herb Ganoderma lucidum, a relatively high cell concentration of 13.8 g center dot L-1 by dry mass was obtained in bioreactor at an impeller tip speed (ITS) of 0.51 m center dot s(-1). At an ITS of 0.51, 1.02 and 1.53 m center dot s(-1), a maximal production titer of intracellular polysaccharide was 2.64, 2.20 and 2.28 g center dot L-1 and that of ganoderic acid was 306, 299 and 273 g center dot L-1, respectively. Under these ITSs, the maximal mean projected area of dispersed hyphae was 3.70, 2.54 and 2.13 x 10(4) mu m(2), and that of pellets was 0.91, 0.67 and 0.55 mm(2), respectively. The information obtained is useful for efficient submerged cultivation of mushrooms on a large scale.