The light-sensitive red-root mutant, designated as HG1, was newly observed from an indica rice variety, Nankinkodo, when seedlings were grown with roots exposed to natural light. The root color of the mutant began to turn slight-red when the roots were exposed to the light at the intensity of 29 μmol/(m2·s), then turned dark-red at the light intensity of 180 μmol/(m2·s), suggesting that the root color of the mutant was evidently sensitive to light. Furthermore, genetic analysis showed that the character of light-sensitive red-root of the HG1 mutant was controlled by a single dominant gene, tentatively designated as Lsr. With simple sequence repeat markers, Lsr gene was located between the markers RM252 and RM303 on chromosome 4 with the genetic distances of 9.8 cM and 6.4 cM, respectively. These results could be useful for fine mapping and cloning of Lsr gene in rice. The light-sensitive red-root mutant, designated as HG1, was newly observed from an indica rice variety, Nankinkodo, when seedlings were grown with roots exposed to natural light. The root color of the mutant began started turn-red when the roots suggesting that the root color of the mutant was evidently sensitive to light (the light at the light at the intensity of 29 μmol / (m2 · s), then turned dark-red at the light intensity of 180 μmol / (m2 · s) ., Genetic analysis showed that the character of light-sensitive red-root of the HG1 mutant was controlled by a single dominant gene, tentatively designated as Lsr. With simple sequence repeat markers, Lsr gene was located between the markers RM252 and RM303 on chromosome 4 with the genetic distance of 9.8 cM and 6.4 cM, respectively. These results could be useful for fine mapping and cloning of Lsr gene in rice.