Sienno [ˈɕɛnnɔ] is a village in the administrative district of Gmina Ostrowite, within Słupca County, Greater Poland Voivodeship, in west-central Poland. It lies approximately 4 kilometres (2 mi) west of Ostrowite, 13 km (8 mi) north-east of Słupca, and 74 km (46 mi) east of the regional capital Poznań.