Citrate, oxalate, tartrate and malate were added into soils during the growth period of ryegrass to study the effect of different organic ligands on the release various inorganic P (Pi) fractions in a yellow-brown soil and a paddy soil. The results showed that oxalate was most effective in promoting the release of total Pi in the yellow-brown soil and tartrate in the paddy soil. The dominant Pi fractions released from the yellow-brown soil were calcium phosphate (Ca-P) and aluminum phosphate (Al-P) and those from the paddy soil were iron phosphate (Fe-P) and reductant soluble phosphate (O-P) mobilized by tartrate. Phosphorous-mobilizing capability of organic acids in the yellow-brown soil revealed the following order: oxalate ＞ citrate ＞ malate ＞ tartrate. In the paddy soil, the order was tartrate ＞ citrate ≈ oxalate ＞ malate. It was demonstrated that organic ligands were different in their capabilities of mobilizing Pi and the same organic ligand showed also a discrepancy in mobilizing P in different soils. Although the addition of organic ligands into soils could increase the amount of P taken up by ryegrass, the more uptake of P, however, was not only due to the more release of Pi, but also partly from organic P. In many cases, organic ligands promoted the release of the total of the total Pi, while different fractions showed different trends: some increased and others decreased.