Mundilfari (Norse: Mundilfäri), or Saturn XXV (25), is a natural satellite of Saturn. It was discovered by Brett J. Gladman, et al. in 2000, and given the temporary designation S/2000 S 9. Mundilfari is about 7 kilometres in diameter, and orbits Saturn at an average distance of 18,360 Mm in 928.806 days, at an inclination of 170° to the ecliptic (150° to Saturn's equator), in a retrograde direction and with an eccentricity of 0.198.
Mundilfari may have formed from debris knocked off Phoebe by large impacts at some point in the Solar System's history.
- IAUC 7538: S/2000 S 7, S/2000 S 8, S/2000 S 9 December 7, 2000 (discovery)
- MPEC 2000-Y15: S/2000 S 1, S/2000 S 2, S/2000 S 7, S/2000 S 8, S/2000 S 9 December 19, 2000 (discovery and ephemeris)
- IAUC 8177: Satellites of Jupiter, Saturn, Uranus August 8, 2003 (naming the moon)