Beta-hydroxy-gamma-trimethyl amino butyric acid (L-carnitine) content of raw and cooked seafood was determined using high-performance liquid chromatography method. Thirty-one different fish species and nine different crustaceans were used to compare L-carnitine content of raw and cooked seafood. Significant differences in L-carnitine content were found in some species, regardless of the raw or cooked seafood (P<0.05). There were also significant differences between some of the raw and cooked species (P<0.05). The levels of L-carnitine in raw fish samples ranged from 17.98mg/kg for big-scale sand smelt to 73.07mg/kg for European conger (Conger conger). Squid (Loligo vulgaris) and green tiger prawn (Penaeus semisulcatus) were found as the best sources of L-carnitine among the tested seafood. Microwave cooking also significantly reduced the L-carnitine content of some seafoods (P<0.05). The study showed that seafoods are an important origin of L-carnitine for covering the daily requirements of humans.