Abstract: We first reported the masculinized feminization gene (fem-1c) in the freshwater pearl mussel Hyriopsis schlegelii, which was cloned by Race-PCR from gonad tissue. Gene structure, multiple sequence homology alignment, transmembrane region, hydrophilia and hydrophobic property, and functional domain prediction was further analyzed using bioinformatics approaches. The full length of fem-1c gene was 2328 bp that contained an open reading frame of 1869 bp encoding 622 amino acid residues. The corresponding protein was stable and hydrophilic. Multiple sequence homology alignment showed that the Fem-1c proteins from H. schlegelii and C. gigas shared the highest amino acid identity (79%). The secondary structure of fem-1c protein mainly contained -helix and random coil forming 9 ankyrin repeat (ANK) motifs. We also found 9 ANK motifs clearly in tertiary structure prediction by SMART soft. The conservation of the fem-1c from invertebrates to vertebrates suggested that these genes have a common ancient origin and that they may play a conserved role in the functions of these organisms. These results suggest that fem-1c gene in Hyriopsis schlegelii may have the similar functions with nematode Caenorhabditis elegans in sex determination.