Cylindrical ingots of 12 different casting and die casting alloys were cast under ambient and 2000kgf/cm2 pressures. The specific gravity, proof and tensile strengths, elongation and impact value of high pressure castings are improved to different degrees corresponding to the casting characteristics of the alloys. The alloys having wider solidification temperature ranges and intensified tendencies to hot shortness show higher relative increase in mechanical properties more significant. The effect of high pressure casting is more pronounced for the alloy having poor castability in such casting indices as hot shortness and pressure tightness that are related to occurance of macroscopic casting defects. Based on the above correlation a new castability criterion including mechanical properties of castings is proposed by evaluating the effect of high pressure casting. The alloys suitable for high pressure casting is discussed based on the present experimental vesults.