A new gridded water-temperature data set of upper 200 m depths (0, 50, 100, 200 m depths) for the Okhotsk Sea was produced using an optimal interpolation technique from 1950 to 1996 using oceanographic observations in the World Ocean Database 1998. Temperature variability at 50, 100 and 200 m depths in the southern Okhotsk Sea (south of 52¿N) in the warm-season (May--October) was investigated by an Empirical Orthogonal Function (EOF) analysis from 1958 to 1994, for which sufficient data exist for an EOF analysis. The first EOF mode has a monopole structure with the maximal amplitude in the Kuril Basin, and the corresponding Principal Component (PC) exhibits prominent quasi-decadal variability. The first EOF mode is closely related with the wintertime (December--February) sea surface temperature anomalies over the subarctic front or Oyashio front in the North Pacific, and with wintertime Sea level Pressure (SLP) differences between northern Eurasia and the northern North Pacific. This suggests that the temperature changes in the Okhotsk Sea are caused by changes in the strength of the Asian winter monsoon, which are associated with the SLP difference. A quasi-decadal oscillation, similar to that of the PC-1, is observed in the SLP difference since the 1960s, and shared by the Polar/Eurasian (POL) pattern, Arctic Oscillation (AO) and North Atlantic Oscillation (NAO). Some hints of the relating variability are observed in coastal sea level difference between Wakkanai and Abashiri, which was used as a proxy for transport in the Soya Warm Current. Also, some features of sea ice extents co-vary with the PC-1.