Soybean seedlings (Glycine max) were exposed to simulated acid rain containing sulfate ion only or a mixture of sulfate, nitrate and chloride anions, using a continuous rain generating system in a side opened glasshouse. Plants were subjected to acid rain treatment twice a week, for a 1 or 3 hr period at a rate of 2.2 or 5.0 mm hr−1, respectively. Dry seed yield in plants treated with simulated acid rain at pH 2.0, in the three of 4 experiments conducted over a 3 yr period, was significantly less than that at pH 3.0 or higher. Simulated acid rain treatment at pH 3.0 or higher did not significantly affect yield compared to pH 5.6; however, plants exposed to simulated acid rain at pH 4.0 tended to yield more than those treated with pH 5.6 rain. Based on the current 3 years of research in which results from 4 experiments were combined, rain acidity at current levels in Japan would not directly affect seed production of selected cultivars of soybean.