Mikołaj may refer to:
In Polish (or Polish-Lithuanian) nobility:
Mikołaj "the Black" Radziwiłł, noble of the Grand Duchy of Lithuania, Palatine of Vilnius, and Grand Chancellor of Lithuania
Mikołaj "the Red" Radziwiłł, Polish-Lithuanian lord, Palatine of Vilnius, Grand Chancellor, and Grand Hetman of Lithuania
Mikołaj VII Radziwiłł, Polish-Lithuanian lord, and Lord Grand Chamberlain of Lithuania
Mikołaj Firlej (?-1526), Polish nobleman, Hetman, diplomat, and expert of south-east Europe
Mikołaj Kamieniecki, Polish nobleman and the first Grand Hetman of the Crown
Mikołaj Krzysztof "the Orphan" Radziwiłł, Polish-Lithuanian lord
Mikołaj Mielecki, Polish nobleman and politician
Mikołaj Ostroróg, Polish nobleman
Mikołaj Potocki, member of the Polish nobility, magnate, and the Field Hetman of the Crown
Mikołaj Sienicki, notable member of the landed nobility of the Kingdom of Poland
Mikołaj Szyszkowski, bishop of Warmia from 1633 til his death in 1643
Mikołaj Zebrzydowski, Palatine of Lublin, Grand Marshal of the Crown, and Palatine of Kraków
In Polish music:
Mikołaj Gomółka, Polish composer
Mikołaj Radomski, Polish composer
Mikołaj Zieleński, Polish composer
In Polish literature:
Mikołaj Hussowski, Belarusian and Polish Renaissance writer
Mikołaj Rej, one of the best known Polish poets and writers of the Renaissance
In other fields:
Mikołaj Kopernik, usually translated as Nicolaus Copernicus, Renaissance mathematician and astronomer, known for formulating heliocentrism
Mikołaj Sieniawski, notable Polish magnate, military commander, and prominent politician
Mikołaj Trąba, Polish Roman Catholic priest, Royal Notary, Deputy Chancellor of the Crown, bishop of Halicz, and archbishop of Gniezno