Abstract: Seawater cultured pearls with dyed nucleus are found in market recently. These are rosy red, orange or bluish gray. Researches reveal that these pearls’ nucleus were dyed before they were input in oysters. After careful research on these pearls together with the ordinarily dyed pearls, the identification features of these pearls are found. Almost all these pearls show the parallel bands under the strong transmitted light, and they do not show any dyestuff concentrated in cracks. Through the drilled hole, coloured nucleus and colourless outer nuclear layers can be seen under magnification. They usually show fluorescence and specific absorption spectrum of dyestuff under UV light and hand spectroscope respectively. Raman spectra tested through the drilled hole reveal that the dyed nucleus show very strong fluorescent background, but the outer nuclear layers do not.