Abstract: Three nitrogen/phosphorus ratios were designed in a sand culture test to analyze the effect of nitrogen/phosphorus ratio on the biological characteristics and organic acid exudation in the roots of soybean. Biomass and nodulation were investigated and organic acid exudation from the roots of soybean was measured with a high performance liquid chromatography. Results showed that at seedling stage, biomass accumulation in soybean was not affected by phosphorus. Suitable nitrogen levels were needed to maintain efficient nodulation. Low phosphorus increased organic acid exudation by the roots of soybean, which was promoted by high nitrogen content. With regards to root organic acid exudation, a negative interaction was noted between nitrogen and phosphorus.