A rice mutant called leafy head (lhd), in which the differentiation of rachis branches is blocked, was identified in a doubled haploid (DH) population derived through F1 anther culture from a cross between rice (Oryza sativa L.) indica cultivar Gui-630 and japonica cultivar Taiwanjing. The mutant is shorter in plant height, possessing smaller and clumpy leaves, and always stays at the vegetative growth stage. Genetic analysis suggests that lhd is controlled by a single recessive gene, which is temporarily named lhd(t). The phenotype of the mutant suggests that LHD(t) is a key gene controlling the differentiation of rachis branches. In order to map the gene, two F2 populations were constructed by crossing the lhd heterozygote with varieties Minghui-77 (indica) and Jinghua-8 (japonica). In the F2 of lhd heterozygote ( Jinghua-8, some mutant plants appeared as the "medium type", suggesting that the lhd phenotype could be influenced by genetic backgrounds. With the published SSR markers of RM series and additional SSR markers developed by ourselves and using the methods of bulked segregant analysis (BSA) and mutant analysis (with 498 mutant plants in total), LHD(t) gene was mapped onto the distal region of the long arm of chromosome 10. Markers SSR1, RM269, RM258, RM304 and RM171 were located on one side with distances of 6.4, 16.6, 18.4, 22.2 and 26.3 cM to LHD(t); whereas markers SSR4 and SSR5 were on the other side with distances of 0.6 and 2.2 cM to LHD(t). The results will facilitate the positional cloning and functional study of the LHD(t) gene.