A laboratory experiment was conducted to study kinetics of sorption of orthophosphate (OP) and pyrophosphate (PP) from dilute solutions by three ammoniated tropical soils. Milligrams of P sorbed by soil (?P) and shaking time (t) showed a linear relationship: ?P = a + b√t. The data suggested two diffusion — controlled processes during P sorption. In general, due to ammoniation, initial sorption rate of OP (in linear region I) increased while that of PP decreased. PP was sorbed more than OP. Sorption rate of OP and PP in linear region II showed a tendency to decrease with increasing ammoniation levels.