Mateusz Masternak (born 2 May 1987 in Iwaniska, Poland) is a Polish professional boxer fighting in the Cruiserweight division.

During Polsat Boxing Night in Łódź, organised on 24 October 2009, Masternak defeated another Polish Cruiserweight Łukasz Janik by technical knockout.

The main event of the evening was a clash between Andrew Golota and Tomasz Adamek which was promoted as "Polish Fight of the Century".

Masternak won by RTD in the seventh round of the bout, defeating Jameson Bostic.

Masternak finished Faisal Ibnel Arrami in the round of eight, winning by technical knockout.

Three months later, on 19 June in Kielce, Masternak beat Lewan Jomardashvili, previously undefeated.

In the fourth round, after series of Masternak's accurate hooks, Jomardashvili was dropped on the canvas two times.

[3] On 12 December 2015, Mateusz Masternak lost the EBU European cruiserweight title bout to England's Tony Bellew (25-2-1, 16KOs) at The O2 Arena, London.

[5] On 20 October 2018, Mateusz Masternak lost in the quarter-final bout of the World Boxing Super Series cruiserweight tournament.