Mikołajki [mʲikɔˈwai̯kʲi] (German: Nikolaikenⓘ) is a resort town in Mrągowo County, Warmian-Masurian Voivodeship in north-eastern Poland, with 3,852 inhabitants as of 2017.

Mikołajki is an old Masurian church town first documented as Nickelsdorf (Sankt Niklas) in 1444 and Niklasdorf in 1493.

In 1454 Polish King and Lithuanian Grand Duke Casimir IV Jagiellon incorporated the region to the Kingdom of Poland upon the request of the anti-Teutonic Prussian Confederation,[3] and the Thirteen Years' War broke out.

Because of its location on Śniardwy, the fishery of Nikolaiken ensured continued prosperity; the whitefish of the region were especially popular throughout the province of East Prussia.

[1] The German-speaking population was evacuated and expelled by Polish and Soviet soldiers in accordance to the Potsdam Agreement.