We investigated the effects of resolved interstitial oxygen or nitrogen atoms and of quenched-in strain on the hardening of the single crystals grown from molten Ti-14 and 20wt pct Mo alloys. The aging treatment at 623K in atmosphere much more increased in the hardness of specimen surface than that in argon atmosphere. The quenched-in compressive stress enhanced age hardening due to omega formation. We surveyed in detail the hardness changes toward the center of plate-shaped single crystal.