These experiments were conducted to investigate the condition of the production and the heat resistance of the acid protease by Rhizopus japonicus S-62. The results obtained were as follows: 1) The optimum concentrations of sucrose, yeast, ammonium chloride and sodium phosphate monobasic added to the wheat bran medium in the acid protease production were 0.5％, 2.0％, 0.4％, and 0.4％, respectively. 2) KH$_2$PO$_4$ and NaH$_2$PO$_4$ were the most effective as the heat resistant agents. 3) When the enzyme solutions added with KH$_2$PO$_4$ and NaH$_2$PO$_4$ to the concentration of 2％ were heated for 10 min, at 50$^{circ}C$, their residual activities were 100％, respectively. 4) The heat resistant effects of KH$_2$PO$_4$ and NaH$_2$PO$_4$ were not observed almost above 55$^{circ}C$.