A chemical study of the winter precipitation was conducted in Tohkamachi, central Japan. The ratios of Ci-/Na+ and Mg2+/Na+ found in the winter precipitation samples are nearly equal to those of sea water. This result suggest that Na+/Mg2+, and Cl- found in the winter precipitation are originated from sea water. A relationship was determined between the Na+ concentration in the winter precipitation sample and the height of the convective mixing layer. Cloud droplets containing sea salt particles are believed to be captured by snow crystals through the rain-out process. The results indicate that the higher the convective mixing layer heights, the larger the amount of sea salt particles captured by the snow crystals. A relationship betwen the Δ18O values in the winter precipitation and the air temperature at the top of convective mixing layer was determined for several synoptic weather conditions that produced winter precipitation. The Δ18O values in samples collected under conditions of winter monsoon are larger than those under other weather conditions at the same temperature. A good relationship is observed between the temperatures at the top of convective mixing layer and the Δ18O of samples of winter precipitation under conditions of the winter monsoon. ¿ American Geophysical Union 1995