9919 Undset is a main belt asteroid. It orbits the Sun once every 3.67 years.
Discovered on August 22, 1979 by Claes-Ingvar Lagerkvist at the European Southern Observatory, it was given the provisional designation "1979 QF1". It was later renamed "Undset" after Sigrid Undset, winner of the 1928 Nobel Prize for Literature.