During 1979 to 1991, relationship between the size of Antarctic krill and the extent of the sea ice in the sea area around the South Shetland Islands are described. Mean size of krill near the coastal zone appeared to be small in summer season just after a strong ice extent had occurred. This implies that strong recruitment of small size krill had occurred just after the season with the strong ice extent. Interannual fluctuations of the ice extent are known to relate with the strength of the Antarctic circumpolar trough. Therefore, it could be suggested climate and ecology of krill populations are closely related.