The castability of base metal alloys for dental casting in influenced by burn-out temperature and recent percentage. Burn-out temperatures for casting are set at 200$^{circ}F$ interval from 1000$^{circ}F$ to 1800$^{circ}F$. According to recast metal percent in new cast alloy metal alloys are tested. The results are as followings: 1. In the new alloy(100%), the castability is the most. 2. The burn-out temperature in 1600$sim$1800$^{circ}F$, castability of 100% new alloy was more four times than of 50% new alloy plus 50% recast alloy. The using of 50% new alloy and 50% recast alloy, therefore, was unlike in castability. 3. The burn-out temperature in 1600$^{circ}F$, castability of 100% new alloy was more than four times in soaking 20 minutes, but there was no any difference at 18700$^{circ}F$. 4. It is investigated that the optimal burn-out temperature is 1600$^{circ}F$ for the C & B alloy.