Female-sterile line can be used as a pollinator which has a great potential for hybrid seeds production. However, reports on female fertility are fewer than male fertility. Here, we characterized a recessive female fertility weakening mutant ff1(t) from rice. The spikelet fertility was seriously affected in the mutant. Reciprocal crosses and pollen vitality assay suggest that the decreased fertility was caused by the defective female gametophytes. Further investigation indicated that the mutant ovary development was inhibited before fertilization and failed swelling after flowering. Genetic analysis and fine mapping showed that the mutant was controlled by a single recessive gene, residing on a 16.8 kb region on the long arm of chromosome 1. The gene annotation indicated that there was only one putative gene encoding lysine decarboxylase-like protein in this region, which was allelic to LOG. Further, the sequence analysis was carried out and a substitution at the splice site of intron 2 / exon 3 was revealed in ff1(t) mutant, resulting in the change of reading frame. The finding of novel allele of LOG locus will facilitate the understanding of the mechanisms of female gametophyte development.