Mielżyn [ˈmjɛlʐɨn] is a village in the administrative district of Gmina Witkowo, within Gniezno County, Greater Poland Voivodeship, in west-central Poland. It lies approximately 6 kilometres (4 mi) south of Witkowo, 21 km (13 mi) south-east of Gniezno, and 58 km (36 mi) east of the regional capital Poznań.