Kochujang, fermented hot pepper soybean paste, was prepared by traditional method, and irradiated with gamma ray of $^{60}Co{;}up{;}to{;}15{pm}1.5{;}kGy$ for confirming main factor of kochujang fermentation. Nonirradiated (control) and irradiated samples kochujang were fermented at $25^{circ}C$ and analyzed biochemical properties including enzyme activities and viable cell count during fermentation for 60 days. The total viable count in irradiated kochujang decreased to $10^4{;}CFU/g$ which was $10^8{;}CFU/g$ in the control. Because of a little changing enzyme activities of ${alpha}{cdot}{eta}{;}amylase$ and acid neutral protease by irradiation at the above level, amino type nitrogen which is the main quality reference of kochujang was comparable to the control. By irradiation, gas production was completely stopped which is one of biggest problems during distribution of kochujang. Total volume of gas produced at $25^{circ}C$ from the control kochujang was 453 mL/100 g which was composed of over 90% of $CO_2$. The odor of irradiated kochujang was inferior to the control which seemed to be related to reduced microbial populations.