The present invention relates to a solid temporal colorimetric hydrogel cosmetic composition having flexibility by irradiation of gamma-rays, and, as an oil-in-water type hydrogel cosmetic composition comprising a water phase part and an oil phase part, is characterized in that the cosmetic composition comprises 15 to 99.90 wt% of the water phase part and 0.10 to 85 wt% of the oil phase part based on the total weight percentage of the composition, the water phase part and the oil phase part have a refractive index difference of 0 to 0.02 therebetween, the cosmetic composition has gamma-rays irradiated thereto, and the cosmetic composition is characterized by a color change according to variations in a refractive index difference between the water phase part and the oil phase difference when applying the cosmetic composition to the skin. A hydrogel cosmetic composition according to the present invention has effects that the cosmetic composition not only has flexibility through irradiation of gamma-rays, but also enables an optimal application time of the cosmetic composition to be visually confirmed through a color change from transparency to ivory white due to a change in the refractive index difference caused by absorbency and volatilization of water when applying the composition to the skin using a refractive index difference between a water phase part and an oil phase part within the composition, and has an effect that the cosmetic composition is capable of improving quality of a product although a preservative irritating to the skin is not added by inhibiting microbial proliferation of a cosmetic material.
