1. This brief report deals with the experiments concerning the difference of the cold resistance between diploid and artificial autotetraploid plants of Brassica chinensis L.. 2. By the degree of wilting (=wilting %-age : number of wilting leaves/number of whole leaves) under low temperature, -2.3°C, the 4x plants were observed clearly to be hardier than the 2x ones. 3. The osmotic pressure recorded in the cells of 4x plants was always higher than that observed in those of 2x ones. 4. No remarkable differences were observed between the 4x and the 2x in the content of water, total nitrogen, and total sugars in the plant tissue. It was, however, recognized that they differed in the soluble sugar content, which might have taken an important roll in causing the difference in their osmotic pressure.