A Laboratory experiment carried out during 2010/2011 at Fac. Agric., MansouraUniv., to study some nutrients availability in clayey soil as affected by magnesium, water content and mineral fertilizers. The used experimental design was spilt-spilt design with three replicated. - Statistical analysis of the obtained results reveal that the content of all Av. nutrients increased significantly in the upper soil section (0-5 cm) with Mg addition, 150% field capacity and fertilizer treatments - Data reveal that the content of all Av. nutrients increased significantly in the lower soil section (5-10 cm) with Mg addition, 150% of field capacity and fertilizer treatments but the content of Av. Ammonium increased insignificantly with adding of Mg. - Data reveal that the increasing percent of all Av. nutrients concentration caused by magnesium and water content under different fertilizer condition. It noticed under different mineral fertilizer treatments that treatment with Mg1W2 gave the highest increasing percentage of all Av. nutrients as compared to control (Mg0W1) in both section. - Data reveal that, the fertilizer treatment F3 application raising the content of Av. K in the first section of soil column. It also shows that the best fertilizer treatments for increase the content of Av. NH₄⁺ and NO₃^- in the first section of soil column were F2. Also with adding of treatment of F5, a highly increase of Av. P content in the first section of soil column high increased in both section. -It can be concluded that the highest mean values of the content of all Av. nutrients obtained from Mg1W2 among all treatment.