Largemouth bass (Micropterus salmoides) is a freshwater fish originating from the United States of America (USA). This specie was introduced in Portugal (Azores) in the end of the XIX Century. Like in the USA, largemouth bass is one of the most popular freshwater sports fish in Portugal and it is very important in regional cuisine, especially in the countryside. However, there’s a lack of information about the chemical composition of largemouth bass fillet. All eaten largemouth bass in Portugal are caught in large dams and small irrigation dams because there’s no largemouth bass aquaculture industry. The aim of this work was to evaluate the chemical composition of largemouth bass fillet collected in an irrigation reservoir (39º49’27.89’’ N; 07º26’57.92’’ W) located in the Central region of Portugal. Thirteen largemouth bass were collected (average weight 349.85g ±74.23; average length 27.22cm ±1.43; average K condition factor 1.71 ±0.14) and were frozen during seven days. The cutting carcasses and the filet chemical analyses (moisture, protein, fat and ash) took place in the laboratory. In the carcass, the average amounts of viscera, spine, head, skin and filet were, respectively, 8.52% (±1.41), 17.24% (±1.29), 23.06% (±1.85), 7.58% (±0.60) and 43.59% (±1.91). In the filet, the average amounts of moisture, protein, fat and ash were, respectively, 77.67% (±1.07), 18.46% (±0.83), 0.90% (±0.31) and 1.20% (±0.05). We concluded that largemouth bass has a good filet yield with very low fat and high level of protein contents. In fact, as far as we know, these are the first results of carcass and filet characterization of largemouth bass collected in Portugal.