Differential GPS observations were conducted on the fast ice in L¿tzow-Holm Bay, Antarctica. The observations were carried out intermittently from April to December in 1998. The vertical displacement, which is a combination of oceanic tidal variation and high frequency variations of 3--6 minutes period, was clearly detected. Eight hours' comparison of the height variation derived from GPS with that from a video monitoring system showed good agreement with a standard deviation of 2.2 cm. The high frequency fluctuations of about 1 cm were obvious in both observations and had significant correlation with each other. The low-pass filtered variations agreed well with a standard deviation of 1.7 cm. Tidal constituents derived from the GPS observations for the entire period showed good agreement with those from the seven years of pressure gauge observations. Thus, GPS has demonstrated the ability to observe 2 cm accuracy sea level variations. ¿ 2000 American Geophysical Union