Light and polarized microscope was applied to authenticate 32 Cordyceps and 6 artificial counterfeits and 8 fermented Cordyceps as well as 7 Cordyceps capsules available in Hong Kong markets. Results showed that transverse sections of stroma and powder of larvae can be used to differentiate C. sinensis from its counterfeits. The fermented Cordyceps are in powder form. Among the eight fermented Cordyceps collected, half of them were pure; three were a mixture of fermented Cordyceps and soya beans; one was a mixture of unknown plant tissues and soya beans. For the seven Cordyceps capsules, the powders of five samples were a mixture of fermented Cordyceps and soya beans; the powders of other two were a mixture of C. sinensis stroma powder and fermented Cordyceps. The study indicated that the microscopy is an unambiguous method that requests fewer sample for the authentication of valuable Chinese medicine-C. sinensis and its related products.