In this work, an in-situ (oxidation) method was used extensively to reinforce aluminum matrix composites with alumina particles. Multi parameters such as alumina particle size and its distribution were studied in details. Side hole diameter, stirring velocity and stirring method were studied also. XRD and SEM tests were used to characterize alumina particles. Results revealed it was obtained on aluminum matrix composites reinforced with alumina particles in Nano size via control side hole diameter and stirring velocity, where the side hole diameter is very effective factor on alumina particle size. The particle size decreases from several microns at (900µm) side hole DIA. to Nano size (≥100nm) at side hole DIA. 500µm with manual stirring. Increasing stirring velocity has led to decrease in alumina particle size which givesthe ability to obtain alumina particles ≤50nm at stirring velocity 2280 RPM with side hole DIA. 900µm. The decreasing in the side hole diameter and increasing in stirring velocity lead to decrease in alumina particles size from several microns toward Nano size, but it has a negative influence on alumina particles distribution.