Uk (, ѹ) is a letter of the early Cyrillic alphabet. It was originally a ligature of the glyphs for "О" and "У" written horizontally. Later it was written more quickly as a vertical ligature (see Ou (letter)), and in modern times has been replaced by the simple "У".

Whilst it no longer appears in the Russian alphabet (or, indeed, any Cyrillic alphabet), its legacy is still there, in the letter Yu (Ю), which was itself a ligature of Izhe (now И) and Uk.