This study was investigated on the change of physico-chemical properties at various mixture ratio of improved Meju and Natto during the aging of soybean paste. pH was increased on the improved Meju with increasing the mixture ratio of Natto, but pH was decreased in Korean traditional Meju. Change of nitrogen compound was 3 times higher and aging was faster in increased ratio of Korean traditional Meju than that of improved Meju. Brown color was not changed as compared to the initial stage, however the value of brown color was higher in the Korean traditional Meju than that of other group. In sensory evaluation, the mixture ratio of improved Meju, Korean traditional Meju and Natto (48 : 48 : 5) was the best acceptables.