Amino acid, vitamin (A, E, B(1), B(2), B(3) and B(6)), and proximate composition were determined in raw and cooked horse mackerel. The changes in amino acid, vitamin, and proximate content were found to be significant for all cooking methods (frying, grilling, and steaming). Cooking did in general significantly increase the contents of essential, semi-essential, and other amino acids compared to raw fish species. Amino acid contents of grilled mackerel were significantly higher (p < 0.05) than those found in fried and steamed mackerel. The A, E, B(2), and B(6) vitamin content of fried horse mackerel was found to be significantly (p < 0.05) higher than the grilled and steamed samples. The B(1) content of steamed and B(3) content of grilled were found higher than the other cooked samples. Moisture, protein, fat, ash, and carbohydrate contents of cooked fish ranged between 56.52% to 61.34%, 20.79% and 23.93%, 13.44% and 19.61%, 1.70% and 2.47%, and 1.02% and 4.36 %, respectively. Fried fish had intermediate fat values, while grilled and steamed fishes had a comparatively low value.