Based on pot experiment with black soil, the effects of various concentrations and various valence of exogenous selenium on soybean yield and its N and P contents and on soil enzyme activities were studied. The results showed that applying 0.25 microgram.g-1 soil and 0.5 microgram.g-1 soil of both Se4+ and Se6+ could increase soybean yield and its N content and promote soil urease activity, but decrease the P content of soybean and soil phosphatase activity. When the concentration of Se6+ was 0.5 microgram.g-1 soil, there was a significantly parabola relationship between the N content of soybean and soil urease activity; and when the concentration of Se6+ was 0.25 microgram.g-1 soil, there was a significantly parabola relationship between the P content of soybean and soil phosphatase activity. There were no significant relationships between the N and P contents of soybean and the activities of test soil enzymes when Se4+ was applied.