This study was conducted to know how cold tolerance of rice varieties is inherited. Several crosses were made between cold tolerant varieties and susceptible varieties, and their progenies were morphologically and physiologically evaluated each characters at cold water and natural conditions. The segregation modes of leaf discoloration by cold treatment in F$_2$ generations are agreed to simple inheritance ratio of R3 : Sl in four crosses among total seven cross combinations. In F$_1$ and F$_2$ generations, tall one was dominance in culm and panicle length and less reduction in culm and panicle length by cold treatment was overdominance or partial dominance, while more number of panicles per plant was dominance and more increasing of panicle numbers by cold water irrigation was overdominance. Heritability and heterosis in most characters showed high values, and heterosis in remote crosses was especially larger under the cold water treatment condition compare with that under natural condition.