The present invention relates to a beverage containing bamboo extract as a main ingredient, for details, a beverage containing bamboo extract as the main ingredient, which is useful for amelioration of diabetes, cancer, life-style related diseases or the like. A beverage characterized in containing, as the main ingredient, bamboo extract obtained through the process comprising the steps by immersing bamboo in water and extracting the bamboo extract with heating the water to 95.degree. C. or higher and maintaining the temperature for a period of 2 hr 45 min to 3 hr 15 min.