Titanium exhibits unique mechanical properties compared to those of other metallic materials.In this study, the stress-strain diagram of titanium casting was proven to be significantly affected by specimen diameter.In particular, total elongation increased markedly with increasing diameter.As for the referential result on a cobalt-chromium alloy, the factor affected the mechanical properties much less than titanium, though the distribution of casting defect was influenced considerably.It was suggested that thermal capacity affected the coagulated microstructure of titanium, which influenced the change in elongation due to the peculiar deformation mechanism of titanium.Since titanium is easily affected by various factors, the mechanical properties of titanium castings should be evaluated with detailed consideration of the specimen configuration, casting conditions, etc.