In order to probe the feasibility of culturing insert-nucleus pearl in visceral mass of freshwater oyster, the different sites of visceral mass were inserted with nucleus in . The morphology, formation and nacre deposition of the pearl sac or insert-nucleus positions were observed after inserting nucleus to confirm inserting-nucleus sites of beneficial pearl formation. The 5 locations in visceral mass were chosen (I: front foot-visceral mass, II: middle foot-visceral mass, III: near reproduction gland, IV: near stomach, V: near kidney), and mussel was inserted nucleus at these locations. The pearl sac of was sampled in the days of 20th, 50th, 90th, and 150th (thd) with operating nucleus, respectively. Then, the formation and pearl formation were observed by the methods of HE staining and paraffin section. were formed firstly in 20thd after inserting , which was secondary pearl sac. Postoperative 50thd, similar pearl sac epithelial cells were formed at inserting nucleus positions of groups I, II and III, while they was not been detected at these positions of group IV or V. The large granular was found at epithelial cells front of groups II and III. Postoperative 90 thd, a large number of intercellular spaces were observed at pearl sac of groups I and III. Epidermal cells with multi-nucleus were increased in groups I and II, and the numbers of granular matter of were increased in epithelial cells of groups II and III. But, the stratified squamous epithelium cells were formed in operating positions of groups IV and V. Postoperative 150 thd, intercellular spaces were decreased in pearl sec of groups I and III. Amass of microvillus were found at epithelial cell free-end of pearl sac in group II. Meanwhile, cell nucleuses were increasing and granular matter were decreasing in groups II or III compared to 90 thd. As the same time, treatmentbut these did not appear in group V. The were breed with inserting nucleus. The nacre was obvious on the inserted-nucleus surface in groups I, II or III at postoperative 50 thd, 90 thd, and 150 thd. the depositional nacre was evenly distributed for groups II and III, but group I did not. The thickness of pearls lay in group II than them in groups I and III <0.05; 0.62 mm±0.07 mm, 0.56 mm± 0.03 mm). Otherwise, there wasn’t nacre deposition on the nucleus surface of groups IV and V. This study confirmed that the formation of the pearl sac epithelial cells existed obviously difference by inserting nucleus in different position of . The complete pearl sac structure could be formed at different sites for middle foot-visceral mass was conducive to pearl growth. This research provided the practical and theoretical foundation for cultivating freshwater pearl in visceral mass.