A method for preparing soap is provided to obtain eco-friendly soap showing a hot spring water-like effect, having an excellent moisturizing effect and causing little irritation. The method for preparing soap comprises the steps of: dissolving 60 wt% of oil and fats extracted from natural vegetables at 50-60 deg.C; mixing 30 wt% of a caustic soda solution containing caustic soda dissolved in concentrated hot spring water with the dissolved oil and fats to provide a soap solution; adding 5 wt% of a fruit concentrate containing 5 wt% of grape seed oil and essential oil and hot spring water to the soap solution; cooling the mixture gradually; aging the mixture for 4-6 weeks at room temperature; and cutting and shaping the aged soap.
