Cooking properties of one variety(Bongui) and two cultivars(KW-12 and KLS-77005-1) were compared. Soybeans were presoaked in distilled water at room temperature for 16 hr and cooked in an autoclave at $106^{circ}C{sim}121^{circ}C$. The cooking rate was calculated by the maximum cutting force of the cotyledons. The cooking time for all cultivars were 150 min at $106^{circ}C$ and 14 min at $121^{circ}C$. The cooking rate constants were similar among cultivars. The z-value which was calculated from the time-temperature combinations that gave the same degrees of cooking for KW-12 was $13.1^{circ}C$ and the others being $11.5^{circ}C$.