An experiment was carried out under laboratory conditions to study the change in available phosphorus (P)‚ magnesium (Mg)‚ calcium (Ca)‚ pH value and EC value during 336 hours of incubation as affected by three levels of each of P and Mg and all possible combination between them in  clayey and sandy soils. Ordinary superphosphate fertilizer as a P-source at rates of 0 (P₀)‚ 13.1 (P₁) and 26.2 (P₂) mg P kg^-1‚ the rates of Mg were 0 (Mg₀), 20 (Mg₁) and 40 (Mg₂) mg Mg kg^-1 as magnesium sulphate. The results indicated that available P‚ Mg and Ca as well as EC were increased with increasing P fertilizers rates‚ while pH was decreased in the two tested soils. Available P‚ Mg and EC were increased with increasing Mg fertilizers rates‚ while available Ca and pH were decreased in the two tested soils. Available P increased up to 12 hours and then decreased with increasing incubation time. Available Mg‚ available Ca and EC increased until 72 hours and then decreased until the end of the experiment‚ while pH decreased until 72 hours and then increased until the end of the experiment.