The present invention relates to an organic/inorganic composite binder composition including a liquid mixture containing PVA as a main ingredient and an inorganic solid powder phase containing calcium hydroxide as a main ingredient. According to the present invention, a functional inorganic material is added to PVA, which is a multi-functional water-soluble polymer, to form a composite, thereby providing a composite material which can be used as an eco-friendly organic/inorganic composite material realizing adhesiveness, waterproof property, flame resistance, antibacterial property, antifungal property and elasticity, and showing a significant decrease in emission of harmful substances and bad odor upon the fire accident. Therefore, the eco-friendly organic/inorganic composite material according to the present invention can be used as an eco-friendly waterproofing agent, eco-friendly paint and an industrial flooring material, in itself, and can be used as an adhesive or a binder with the other various materials to provide various types of heat insulation panels, buoys, or the like.