The snow on the sea ice controls the energy exchange because it has the insulative property between the atmosphere and the sea ice, and influences the albedo in the sea-ice region. Therefore, the snow on the sea ice is very important for understanding sea-ice change. Though site observations with a microwave radiometer are effective for snow on sea ice, cases are few. This study aims to observe the microwave brightness temperature of the snow on sea ice and to clarify the characteristic. We observed the snow and sea ice in Saroma Lagoon. The structure and the salinity of the sea ice in Saroma Lagoon are reported to be the same as general sea ice from a current observation. The brightness temperature of the snow on sea ice measured the H-pol and V-pol of 18 and 36 GHz. The incidence angle is 55°. The brightness temperature of snow on the sea ice is higher than that of free snow sea ice. The H-pol are larger than the V-pol in both states. In the H-pol, there was a point where the brightness temperature changed to 20 K or more, too. Then, it was examined by comparing the observed brightness temperature and the model calculation result for the snow on the sea-ice amount estimation. The density, grain diameter and water content were changed respectively and simulated. The radiation from the sea ice was assumed to be constant. The brightness temperature tends to decrease by the volume scattering when the dry snow. On the other hand, the brightness temperature increased in the snow in which the water content is 10%. From these results, the observed snow has the possibility that is the wet snow. When the H-pol was compared with the V-pol wave, the H-pol was shown to have received the influence of a permittivity difference in the snow and the sea-ice boundary layer strongly. Moreover, the wet snow made the brightness temperature of the H-pol change more than dry snow. From these results, it was clarified that the water content of snow and change of permittivity in the interface of sea ice and snow influenced the microwave emission of snow on sea ice.