Floral organ is the basis of seed growth， and the development of rice floral organ directly affects the yield and quality. An open-hull mutant （oh） was found in the progenies of rive cultivar Yuanmeisimiao crossed with P704. The oh mutant displayed abnormal floral organ with unclosed lemma and palea， decreased seed setting rate and smaller seeds. Genetic analysis showed that the open-hull phenotype was controlled by a pair of recessive nuclear genes. Using bulked-segregant analysis （BSA） method， the open-hull gene was allocated in the interval 22806614~23000408 on rice chromosome 3， where the OsMADS1 gene （LOC_Os03g11614） is present. Through alignment with the homologous gene in the Shuhui498 reference genome， the nucleotide transversion （aspartic acid to tyrosine） at the 118^th nucleotide of the first exon of OsMADS1 in oh was identified （designated OsMADS1^oh）. OsMADS1^oh was cloned from oh and used to construct overexpression vector. The overexpression vector was introduced into the transformable material （ZH11） by Agrobacterium-mediated transformation. The lines over-expressing OsMADS1^oh showed the open-hull phenotype. In addition， the RNA expression results of real-time quantitative PCR showed that the expression of MADS8 and YABB5 were regulated by OsMADS1. Collectively， this study approved the OsMADS1^oh， as a new allelic variant of OsMADS1， and provided specific resources for elucidating the molecular mechanism of floral organ formation.