As a study on the acid protease production by Rhizopus japonicus S-62, the culture conditions for the enzyme production and characteristics of the crude enzyme were investigated. The results are summarized as follows: 1. The optimum conditions for solid culture on wheat bran were 48 hrs of culture period and $100{sim}120%$ addition of tap water. 2. Of the several media, wheat bran medium was the most excellent in the enzyme production. 3. The addition of sucrose, fructose, $NH_4Cl$ and $NaH_2PO_4$ on wheat bran, respectively, increased largely the enzyme production. 4. The optimum pH for the enzyme action was pH $2.4{sim}2.6$, the optimum temperature was about $40^{circ}C$, and the stable pH range was $pH;2.5{sim}5.0$, the enzyme was stable below $40^{circ}C$ and was inactivated abruptly above $40^{circ}C$.