Infrared reflectance spectroscopy was used to test six kinds of plastic imitation materials for gems in jewelry market. Those materials were compared with the corresponding six real gem materials including pink coral, ivory, rhodochrosite, green chalcedony, rock crystal and synthetic black opal. The results showed that the infrared spectra of plastic imitations were significantly different from those of real gemstones due to the differences in material composition and molecular structure. Infrared spectroscopy not only could identify and classify plastics according to the number, position, morphology, strength and spectral division of infrared spectral peaks, but also was a quick, accurate and nondestructive means for testing plastic imitations. In particular, for the identification of those high imitation products with appearance and basic physical characteristics quite similar to their corresponding real stones (such as imitations for synthetic black opal), conventional identification means were not effective, but infrared reflectance spectroscopy could play an irreplaceable role.