The organic matrix proteins of molluscan nacre are known to engage biocompatible and osteoinductive properties. In this study, we aimed to extract Haliotis diversicolor nacreous proteins and assayed their effect on pre-osteoblastic cell differentiation. We found that acid extracted nacreous proteins (AEP) consisted primarily of a major protein band of 25 kDa and three other minor proteins. AEP enhanced alkaline phosphatase (ALP) activity of MC3T3-E1 cells both in time- and concentration-dependent manners. Transcriptional up-regulation of osteogenic markers, including collagen type I (COL-I), osteopontin (OPN) and osteocalcin (OCN), was also apparent in days 7 and 14 upon AEP treatments. At the translational level, higher protein expression of COL-I was evident in AEP treated cells, and the protein was presumably laid down as extracellular matrix. Further de novo sequencing of an AEP major protein revealed a match with the abalone mantle protein sometsuke. Conclusively, we demonstrated that H. diversicolor AEP contains a factor, potentially the mantle protein sometsuke, which may impart in the osteoblastic cell differentiation.