Abstract: Background and Objective: Availability of adequate phosphorus (P) for plant uptake is a major problem in acid soils worldwide. Characterization of soils in terms of phosphorus (P) sorption capacity is, therefore, fundamental for effective soil phosphorus fertility management and for efficient utilization of phosphorus fertilizers. A study was conducted to investigate the phosphorus sorption characteristics of selected acid soils from Meru, Embu, Kirinyanga, Nyeri, Kiambu and Kinangop and evaluate the external phosphorus requirements (EPR) for soil phosphorus fertility management. Materials and Methods: Sorption data was obtained by equilibrating the nine soil samples with 30 mL of KH2PO4 in 0.01 M CaCl2, containing 0, 80, 100, 150, 180, 200, 250 and 300 μg mL–1 for 48 h with shaking for 30 min at intervals of 8 h. Langmuir adsorption model was fitted to the test results and relationship between P Langmuir adsorption model was fitted to the test results and relationship between P adsorption Langmuir constants and soil properties determined by simple regression and correlations using Genstat statistical software. Results: The result of this study showed that the Nitisols were extremely acidic (pH 3.7-4.5), had low extractable P (<15 mg kg–1 Bray 1) and the maximal phosphorous adsorption varied from 2986.73-2992.58 mg kg–1 soil. The external phosphorus requirement (EPR) varied from 434.78-208.33 mg kg–1 soil in the order: Nyeri = Embu>Kirinyanga>Meru = Kiambu>Kinangop. Correlation analysis revealed that Langmuir adsorption maxima (bL) and binding energy constant (kL) positively correlated with clay content and EPR and negatively correlation with organic carbon and soil pH. Conclusion: Due to differences in phosphorus fixation rates EPR within the study sites, different phosphate fertilization rates are required for optimum plant growth in such soils. Also management practices involving the use of organic matter and liming as basis for P adsorption reduction would be useful for improved crop production in the soils. There is, therefore, need for further research to determine optimal phosphorus requirements for soils in each research site under field conditions.