Abstract: A method of HPLC combined with immunoaffinity column cleanup and post-column photochemical derivatization was applied to determine aflatoxins G2, G1, B2 and B1 in platycladi seeds, which was a kind of Chinese herbal medicine. The sample was extracted with methanol (7+3) solution, then the extraction was purified by immunoaffinity column and the analyte was eluted by methanol. The eluent was separated on a special C18 chromatographic column for aflatoxins with a methanol (45+55) solution as mobile phase. The wavelength of post-column photochemical derivatization was 254 nm, and the excitation wavelength and emission wavelength of fluorenscence detector were 365 nm and 440 nm, respectively. The linearity ranges of aflatoxins G2 and B2 were both 0.125-5.0 μg·L-1, and the linearity ranges of aflatoxins G1 and B1 were both 0.50-20 μg·L-1, with detection limits (3S/N) in the range of 0.012-0.047 μg·L-1. Recovery rates obtained by standard addition method were in the range of 81.4%-105% and RSDs (n=6) were in the range of 1.6%-6.9%.