This research is trying to identify the contribution of some different organic and inorganic materials besides alternating wetting and drying process in soil aggregates formation and stability. A laboratory incubation experiment was conducted to achieve this purpose, sandy soil was chosen for this study. The incubation treatments included inorganic materials; calcium sulfates and ferrous sulfates and some organic materials; humic acid and plant residues. These materials were added only and with 10 % clay, also, the treatments conducted to drying/wetting cycles and without. The findings of this experiment showed that the soil aggregates formation and stability depended largely on the interaction between organic materials and clay content under drying/wetting cycle's effect. The higher contribution percentage was 9.2 % for humic acid plus 10 % clay after drying/wetting cycle's treatment compared with the control.