We hypothesized that bacterial siderophores were partially responsible for P solubilization from FePO4. This hypothesis was supported by the strong correlation (r2 = 0.94) between bacterial siderophore-production and P solubilization from FePO4 (Table 1). After boiling, the spent media of PG4 did not lose its ability whereas other 6 strains lost 7.2–30% of their ability in P solubilization (Table 1). Though PG 5 and 12 were most efficient in P solubilization from both phosphate rock (65–84% enzymatic) and FePO4 (27–30% enzymatic), siderophore probably played a more important role in solubilizing FePO4 (Table 1). However, the data indicated that, besides siderophores, enzymatic process also played a role in P solubilization. Extracellular enzymes exuded by rhizobacteria have been found to improve plant growth and P uptake