Solidification conditions and mechanical properties of unidirectionally solidified 356 alloy were studied by means of stepwise regression analysis. The elongation of as-cast alloy is strongly affected by average cooling velocity in the solidification range and temperature gradient. 0.2% proof stress is negatively affected by temperature gradient and moving velocity of solid-liquid interface. Partial cooling velocity from liquidus to the temperature at which 40% volume fraction of solid has solidified has a significant effect on ultimate tensile strength, Brinell hardness, maximum load, crack initiation and propagation energy, and total absorbed energy in instrumented impact test. As to T6 treated castings, partial cooling velocity has an effect on tensile and impact properties except maximum load. Maximum load, crack initiation energy and total absorbed energy are strongly affected by moving velocity of solid-liquid interface.