In the present paper, the effect of the parameters of cooling slope casting (CSC) process on the microstructure of A356 cast aluminum alloys were studied. The parameters considered are pouring temperature (T), cooling slope length (L) and tilt angle (θ). The analysis of variance (ANOVA) was carried out to clarify the relationship between the aforementioned parameters and the microstructure variables: includes shape factor (S.F.) and grain size (G.S.) of the α-Al primary phase. Moreover, the uniformity of the microstructure in both the axial and radial positions of the ingots was also examined. The results explained that the tilt angle has the highest significant effect and the cooling slope length has a medium effect on both shape factor and grain size. It was also found that the pouring temperature has the lowest effect on shape factor and has a medium effect on grain size. The investigations showed that the maximum value of the shape factor is 0.8119 at θ= 30o, L = 300 mm, T= 630 oC and its minimum value is 0.7149 at θ= 60o, L = 200 mm, T = 640 oC. Regarding the grain size, it was found that the maximum value is 59.82 µm at θ= 30o, L = 200 mm, T = 620 oC, where its minimum value is 32.85 µm at θ= 60o, L = 200 mm, T = 630 oC. Moreover, the maximum uniformity in the shape factor was assured at θ= 30o, L = 400 mm, T = 620 oC, while that of the grain size was confirmed at θ= 60o, L = 300 mm, T = 630 oC