This paper explain the impact of varying amount of reinforcement on mechanical and micro-structural properties during the fabrication of Al2O3-LM6 cast composite at self-pouring temperature. To decide the reinforcement proportion, use of mixture design of approach was used. Fine triturates of Al, Si, and xAl2O3 (x = 2%, 3%, and 4%) were mixed firstly by using ball milling. Then powder mix, which was pre-heated and became moisture free, condensed in sealed steel die. Compacted pre-forms were heated in a muffle furnace in the presence of Argon gas which creates an inert environment at self-poring temperature deprived of forming liquid slurry to pour under gravity in the cavity of Plaster of Paris (POP) die to synthesize the final cast composite. Blend combination was decided using mixture Design of Experiment (DOE) through Minitab Software and an Analysis of Variance (ANOVA) was performed to heighten the best mixture combination. Then fabricated modified cast composite then tested to show a combined outcome of reinforcement proportion on modified physical, mechanical and micro-structural properties.