Seeds of soybean [Glycine max (L.) Merr, var, Bay] were irradiated with X-ray (21.4 kR), and the M(2) generation was evaluated for palmitic acid content in the seed oil, The X-ray irradiation significantly increased the genetic variability of palmitic acid content in the oil of the Bay variety as compared with the control plants, Among the 2064 M(2) plants tested, two mutants were selected in which the palmitic acid contents accounted for 5.7 and 16.6%, respectively, about two-fold lower and 1.5-fold higher than that of the original variety. The mutants J3 and J10 always had lower and higher palmitic acid, respectively, under different environmental conditions in the M(3) and M(4) generations.