Water chestnuts and black water chestnuts were dried and milled to analysis their nutrient compositions. The results showed that polysaccharides in water chestnut and black water chestnut were composed of glucose, D-galactose, and D-arabinose, while the D-galactose content in black water chestnuts was higher. The amino acids profiles showed that water chestnuts contained 11 kinds of amino acids, and the black water chestnuts contained 13 kinds of amino acids. The main nutrients in black water chestnut were protein, fat, reducing sugar, and polysaccharides. Compared with water chestnuts, black water chestnuts contained more P, Fe, Na, and Ca, while the contents of flavonoids, polyphenols and black extracts were higher. The results showed that the nutrient and functional active components were higher in black water chestnuts, so black water chestnuts can be used as a new material to increase the added value of the products.