Nikolaj is a given name (in most cases Николай, Slovene form of Nicholas transliterated to Danish or other Scandinavian language), and may refer to:
Nikolaj Abraham Abildgaard, Danish artist
Nicolaj Agger, Danish professional football player
Nikolaj Coster-Waldau, Danish actor
Nikolaj Frederik Severin Grundtvig, Danish teacher, writer, poet, philosopher, historian, pastor and politician
Nikolaj Gavric, footballer from Switzerland who currently plays as midfielder for FC Concordia Basel in the Swiss Challenge League
Nikolaj Koppel, Danish musician
Nikolaj Hansen, Danish football player
Nikolaj Hübbe. balletmaster of the Royal Danish Ballet and former principal dancer at the New York City Ballet
Nikolaj Nyholm, Danish serial technology entrepreneur and investor
Nikolaj Znaider, Danish violinist