Type I collagen is commonly used in medical materials and cosmetics. While it can be extracted from the skin and bones of mammals, marine collagen has attracted attention recently, since the use of mammalian collagen could result in zoonosis, and products containing mammalian collagen are avoided due to some religious beliefs. Chemical extractions using strong acids and alkalis, thermal extractions, and other nonconventional methods have been used for collagen extraction. However, there are few reports on environmentally friendly methods. Although heat extractions provide higher yields of collagen, they often cause collagen denaturation. Therefore, dilute acetic acid and ultrafine bubbles of oxygen, carbon dioxide, and ozone were used to extract type I collagen from tilapia scales. The extraction performance of the different conditions employed was qualitatively analyzed by SDS-PAGE electrophoresis, and the collagen concentration was quantified using circular dichroism spectroscopy by monitoring the peak intensity at 221 nm, which is specific to the triple helix of type I collagen. Collagen was extracted from tilapia scales with a yield of 1.58% by the aeration of ultrafine bubbles of carbon dioxide gas in a 0.1 M acetic acid solution for 5 h.