Abstract: A dwarf and more-tiller mutant (dmt) was obtained from the ethyl methanesulfonate (EMS) mutant library of Kongyu131 (Oryza stativa ssp Japonica cultivar). The dmt mutant exhibits decreased plant height, more tillers and smaller grains. Genetic analysis indicated that the dmt phenotype is caused by a single recessive mutation. The Strigolactones (SLs) analogue GR24 could restore the dmt phenotype, indicating that SLs biosynthesis pathway of dmt was disrupted. Combining bulked segregant analysis (BSA) and MutMap analysis, LOC_Os04g46470 encoding a carotenoid cleavage dioxygenase 7 (CCD7) was identified as a candidate gene for the dmt. Sequence analysis revealed a G-to-A transition point mutation at the last base of the fifth exon of LOC_Os04g46470 in the dmt, resulting in a frame shift with the fifth intron transcribed. Moreover, the CCD7 transcript level in the dmt mutant was significantly higher than that in the WT, supporting the negative feedback role of CCD7 in SLs biosynthesis regulation.