Abstract: Isoflavones are a group of important secondary metabolites accumulated in soybean plant (Glycine max Merri) especially in seeds, and have a lot of important functions. The accumulation of isoflavones in soybean leaves can be induced by light. Our experiments aimed at the soybean phenylalanine ammonia-lyase (PAL) gene expression under different light conditions. It was found that expression of pal in light was higher than that in darkness. The effects which depend on different varieties was more sensitive to light in the variety which has lower contents of flavones in seeds. Red light (R), Blue light (B) and UV light (UV) increased PAL mRNA abundance, and UV was the most effective light. With the elongation of treatment time, the mRNA abundance for pal and activity of the enzyme increased. The isoflavones accumulation showed to decline with the UV time. This pattern was not consistent with that at the level of mRNA and the enzyme.