In the study, one chromosome single segment substitution line, CSSL182 which developed from cultivated rice 9311 as the receptor parent and Oryza rufipogon as the donor parent, was selected for grain shape QTL identification. The CSSL182 has significant shorter grain width and lighter grain weight compared with receptor parent 9311. Using a CSSL182/9311 F2 population, one QTL associated with grain width, which named qGW8, was identified that located between RM447 and RM264 on Chr. 8. Using additional molecular markers, 2000 F2 individuals and F3 recombinant plants were detected and then qGW8 was finally fine mapped to a 10KB region. DNA sequencing found that 3 genes were located in this region. The scanning electron microscopes detection showed that width of CSSL182’s glumes cell was 16.7% narrower than 9311’s, indicated that the alleles from wild rice might controls grain width by affecting glumes cell shape.