Two phosphate rocks (PRs) from Sri Lanka and Togo were acidulated with 5 M of citric, oxalic or tartaric acid at 2:1 acid:rock ratio for three days. The resulting materials treated with oxalic and tartaric acid were easily dried up and nearly all the P was in water soluble form. The PRs treated with citric acid were rather difficult to dry and contained about 50% of the total P in water soluble form. The effectiveness of the materials as phosphorus sources were compared with that of single superphosphate in acidic granitic regosol with Italian ryegrass as the test crop. All the acid treatments were as effective as single superphosphate in increasing the dry matter yield of Italian ryegrass at 168 days after planting except the citric-acid treated Sri Lanka PR. Phosphorus recovery by the plants from tartaric-acid treated Togo PR was 58%, which was significantly greater (P<0.05) than those from single superphosphate (52%) and tartaric-acid treated Sri Lanka PR (53%). Significantly higher levels of available P (OLSEN P) and pH were found in the cropped soils which received the organic-acid treated PRs than those of the soils which received single superphosphate and control at the end of the experiment. No adverse effect of the organic-acid treated PRs on the growth and nutrient uptake by Italian ryegrass was observed throughout the growth period. These results indicate that at least the tartaric-acid treated PRs could be better sources of P to crops growing on acid soils than single superphosphate.