Plastochron and phyllotaxy are important traits to determine plant architecture. A plastochron 1-6 mutant was derived from japonica rice cultivar Koshihikari treated with ethylmethane sulfonate (EMS). The plastochron 1-6 mutant showed reduced plant height, shorter internode length, smaller and more leaves than Koshihikari, its wild type. In addition, the mutant has abnormal panicle, abnormal seed and upper node tillers. The F1 plants between mutant and Koshihikari were normal. In F2 population, segregation ratio between the wild type and mutant was fitted to 3:1. This genetic analysis indicated that plastochron 1-6 is controlled by a single recessive gene. Bulked segregant analysis revealed that the gene was located on chromosome 10. Through sequencing analysis, we found that plastochron 1-6 mutant had a single nucleotide transition occurred in the first exon of LOC_Os10g26340 (encoding P450 CYP78A11). This work was supported by a grant from the Next-Generation BioGreen 21 Program (Plant Molecular Breeding Center No. PJ008125), Rural Development Administration, Republic of Korea.