Hermaszewski has been interested in aviation and model aircraft since an early age. He is married to Emilia (née Łazar) Hermaszewska since 1966 and together they have two children, Mirosław (born 1966) and Emilia (born 1974). He has three grandchildren: Julia, Amelia, Emilia, and Stanisław as well as a pet Yorkshire Terrier Giokonda. Hermaszewski's son, Porucznik Mirosław Roman Hermaszewski, on his career path followed the footsteps of his father and uncle, graduating from the Polish Air Force University to become a military reserve force officer. Hermaszewski's daughter married politician Ryszard Czarnecki.