Isachsenfonna is a plateau glacier in Haakon VII Land at the northwestern part of Spitsbergen, Svalbard. It covers an area of about 140 km², and reaches a height of about 900 metres above sea level. The glacier is named after polar scientist Gunnar Isachsen, who traversed the glacier in 1906.
Coordinates: 79°10′08″N 12°52′58″E / 79.1689°N 12.8829°E