A method for the determination of low molecular weight organic acids in roots,stems and leaves,and root exudates by ion chromatography (IC) was established,and the varied characteristics of low molecular weight organic acids in roots,stems and leaves,and root exudates of four species seedlings were detected,which provided evidence for revealing the role of organic acids in plant.The recoveries and detection limit of low molecular weight organic acids were in the range of 91.10%～105.42% and 0.12～0.36 mg/L,respectively.The determination coefficient of linear equation (R²) ranged from 0.965 3～0.998 8.Oxalic,citric,malic,succinic and tartaric acids were determined by IC in roots,stems and leaves,and root exudates of four plant species.Oxalic,citric and malic acids were the dominant organic acids.The composition and concentration of organic acids were influenced by plant species and organ,the interspecific differences were in the organic acids concentrations between root exudates and roots,stems and leaves.The results provided a reliable method for study organic acids of plant organ and root exudations,and provided evidence for understanding the role of organic acids in plants under environmental stress.