A thermo-sensitive seedling-colour mutant 7436S was detected in the field from a breeding nursery in China, in 1991. The experiments were conducted at artificially controlled temperatures (23.1°C, 26.1°C, 30.1°C) in growth chambers. The results showed that the seedling colour of the mutant 7436S was white (23.1°C), light yellow (26.1°C) and normal green (30.1°C) at 10 days after sowing and yellowish green (23.1°C) and normal green (26.1°C, 30.1°C) at 20 days after sowing, respectively. It was concluded that its thermo-sensitivity decreased gradually with the increase of the seedling age. In addition, its thermo-sensitivity for seedling colour was oriented, as white seedlings turned green at high temperatures, but not in the opposite direction. The segregation ratios in the F₂ populations showed that a recessive nuclear gene (tentatively designated as tsc-1) controlled the thermo-sensitive seedling-colour character. Based on genetic linkage and the recombination value (34.1%) between the tsc-1 gene and short panicle morphological marker (sp) gene in the F₂ generation, the results indicated that the tsc-1 gene was located on chromosome 11.