A method was improved for the determination of phosphomonoesterase activity in red soils by determining inorganic phosphate released from soil incubated with Na-β-glycerophosphate as substrate. The influence of inorganic P adsorption on soil can be greatly minimized by the pretreatment that the substrate was mixed with appropriate inorganic P before being added into the soil for incubation. The proposed method successfully determined phosphomonoesterase activities in 4 red soils. The results showed that the precision of the proposed method (RSD ≤ 3.7%) was greater than that of Rogers method (RSD ≤ 10.2%). Compared with Rogers method, the proposed method avoided HCl extraction procedure and shorted analytical time from 19 hours to 2 hours. In addition, phosphomonoesterase activity obtained with the proposed method ( P 4.4 - 6.8 μmol/(g soil·h)) was significantly higher than that obtained from the p-nitrophenyl phosphate method ( P 0.8 - 2.2 μmol/(g soil·h)).