Fish processing industries worldwide are discarding million kilograms of fish waste per year. The disposal of these wastes is an important handicap in fish processing industry. The thick eel skin is considered a waste product in the fish processing industry and in the home and is usually converted into low market-value products. The aims of this study were to evaluate the variations in the general chemical composition and amino acid content of eel skin in relation to body weight. The moisture content decreased and the lipid content increased with the weight of the eels. Eel skin had a high protein content, which did not vary significantly with eel weight. Glycine was the most abundant amino acid. The predominant essential amino acid was leucine. The smaller eels contained higher levels of threonine, valine, isoleucine, leucine, lysine, glutamic acid and tyrosine than the other groups. The larger eels contained higher levels of methionine, hydroxyproline, glycine, arginine, alanine and proline than the other groups. The protein indices showed that the skin from smaller eels was of higher nutritional quality. Graphical abstract