The effects of NH4+-N and NO3--N applications on rhizosphere pH and P uptake were investigated with and without mycorrhizal inoculation. Sorghum (Sorghum bicolor L.) plants were grown in split pots and in different soils with different initial soil pH values and P contents. In both soils, ammonium treatment resulted in higher plant dry weight and P content than nitrate treatment at all P levels. Mycorrhizal inoculation enhanced the differences. Sorghum plants acidified the rhizosphere at low soil P status with both nitrogen forms, and with or without mycorrhiza. When N was supplied as NO3--N, rhizosphere pH increased gradually with increasing P addition.