Many studies have been conducted on the methods of collagen extraction from fish skin. However, the specific composition of the collagen has not been reported so far. This study aimed to identify components other than amino acids in collagen. Collagen was extracted from the skin of tilapia (Oreochroma niloticus), flounder (Paralichthys olivaceus), and red sea bream (Pagrus major) using a commonly used acid extraction method. Thereafter, the component composition of collagen was confirmed. The yield of collagen was 1.11% from tilapia, 1.79% from red sea bream, and 2.06% from flounder. The protein content of all three samples, tilapia (85.39%), red sea bream (87.48%), and flounder (92.06%) collagen was over 85%. Analysis of the amino acid composition revealed that, glycine accounted for the highest proportion in all the samples of fish skin and collagen. The imino acid content was highest in the tilapia skin (151.1 residues) and collagen (210.7 residues). The triglyceride content in the of collagen was less than 0.7% in tilapia (0.37%), sea bream (0.61%), and flounder (0.31%). The major fatty acids in collagen were palmitic acid, stearic acid, and nervonic acid. Calcium in the fish skin accounted for the highest proportion of the mineral composition at 23.96∼466.84 mg/100 g, and the collagen contained a large amount of sodium 189.28∼1,433.52 mg/100 g. The collagen contained galactose, glucose, and mannose, and the galactose and glucose levels were three times higher than those of fish skin. Our study confirmed that the collagen extracted from fish skin contained lipids and minerals even though it was purified.