In this study, -Al2O3 short fibers (0%-30 %) reinforced Al-12Si (wt-%) LM-13 aluminum composites formed by gas pressure infiltration method were used. In the literatüre; the standard aging heat treatment of LM-13 aluminum alloy is given as solutionizing at 515 °C for 8 h. And aging at 171 °C for 12 h. Prior experiments on these composites have shown that this aging treatment was not sufficient to get the intermetallics, that to be precipitated during aging, could not be solved by the standard solution temperatures and times. For this purpose, different heat treatment parameters have been tried to clarify the effect of the reinforcing element on the matrix phase precipitation in these composites. The aim of the work was to study the effect of - Al2O3 short fibers and aging heat treatment on the bending strength of the composites. Unreinforced alloy and the composite samples have subjected to three-point bending tests and the shear strength values were measured. Measurement of bending strength with scanning electron microscopy studies show that the biggest value of bending strength increment for unreinforced and -Al2O3 short fiber reinforced LM13 alloys are very different. Initial studies have shown that the solution take-up temperature of 535 is ideal for maximum bending strength. For this reason, the composites and unreinforced alloy specimens were solution treated at 535 °C temperature for 8, 12, 16 and 20 hours and quenched in water at 20 °C. Aging was carried out at four aging temperatures of 151, 161, 171 and 181°C for a varying time of up to 22 h in air. The results revealed that at the optimized aging heat treatment conditions have given higher bending strength results when compared with standard aging treatment. For example, optimum heat treatment for 30 pct -Al2O3/ Al-12Si composite the optimum heat treatment was recorded as follows; solution treatment at 535°C for 20 hours and artificial aging at 151°C for 14 hours. The fracture surface investigations that performed by secondary electron images by scanning electron microscopy (SEM) showed that the fibers are bonded very well to the matrix and the phenomenon of fiber pull-out from the matrix is minimum at the optimum heat-treated composite samples.