Olsza [ˈɔlʂa] is a village in the administrative district of Gmina Mogilno, within Mogilno County, Kuyavian-Pomeranian Voivodeship, in north-central Poland. It lies approximately 4 kilometres (2 mi) south-east of Mogilno, 54 km (34 mi) south of Bydgoszcz, and 61 km (38 mi) south-west of Toruń.