In the present paper, the effect of cooling slope casting (CSC) parameters, typically, pouring temperature (T), cooling slope length (L) and tilt angle (θ), on the microstructure of A356 cast aluminum alloys was studied. The analysis of variance (ANOVA) statistical technique was carried out to explain the relationship between the aforementioned parameters and the microstructure variables of the α-Al primary phase such as the shape factor (SF) and the grain size (GS). The uniformity of the microstructure in both the axial and radial positions of the ingots was also evaluated. The results revealed that the tilt angle has the highest significant effect on both shape factor and grain size. The shape factor exhibited maximum value of about 0.812 for ingots poured at θ = 30º, L = 300 mm, T= 630 ºC. The minimum grain size was about 32.85 µm for ingots casted at θ = 60º, L = 200 mm, T = 630 ºC. Ingots poured at θ = 60º, L = 300 mm, T = 630 ºC exhibited the highest grain size uniformity. While ingots casted at θ = 30º, L = 400 mm, T = 620 ºC, investigated the highest shape factor uniformity.