Plant height and tillering, which served as two of important agronomic characters of rice, can determine the final yield. In this study, one genetically stable and high-tillering dwarf mutant t489 was identified from the tissue culture seedlings of ‘Nipponbare’, a japonica rice variety. Compared to the wild type, the mutant t489 showed semi-dwarf and high-tillering. The genetic analysis indicated that this phenotype was controlled by one single recessive gene. Sequence analysis of D17/HTD1 allele in the t489 mutant showed G-to-T substitution at the 916’ of the coding sequence, which caused premature termination of the D17/HTD1 encoded protein. D17/HTD1 encodes the carotenoid cleavage dioxygenase 7 (CCD7), which is one of the key enzymes in the biosynthesis pathway of plant hormone strigolactones (SLs). d17 allele encodes for a truncated protein containing 305 amino acids, while no difference on the expression level was detected in the t489 mutant. Furthermore, a molecular marker dCAPS-D17 based on the G916T mutation site was developed. By tests in BC1F2 population derived from the t489 mutant and ‘Nipponbare’, this marker was co-separated with the dwarf and high-tillering plant. Taken together, these results suggested a new d17/htd1-allelic mutant in mutant t489.