Monthly estimates of the Earth's gravitational field from the GRACE mission are used to construct a time‐series of global mean ocean mass variations between August 2002 and December 2003. This time‐series is compared to a mean climatology determined from satellite altimeter measurements of global mean sea level corrected for the steric variation. The GRACE observations show a seasonal exchange of water mass with the continents of the same magnitude (∼8.5 mm) and phase (maximum in early‐ to mid‐October) as the steric‐corrected altimetry. This is one of the first direct validations over the ocean of the primary GRACE science mission to measure time‐variable transports of water mass in the Earth system, and it suggests that GRACE data can be used to measure non‐steric mean sea level variations which is important for climate change studies.