Nacre or mother of pearl is a calcified structure that forms the lustrous inner layer of some shells. We studied the biological activity of the water-soluble matrix (WSM) extracted from powdered nacre from the shell of the pearl oyster, Pinctada maxima, on the MC3T3-E1 pre-osteoblast cell line from mouse calvaria. This cell line has the ability to differentiate into osteoblasts and to mineralize in the presence of beta-glycerophosphate and ascorbic acid. Cell proliferation and alkaline phosphatase activity were measured as markers of osteoblast differentiation, and mineralization was analyzed. These studies revealed that WSM stimulates osteoblast differentiation and mineralization by day 6 instead of the 21-day period required for cells grown in normal mineralizing media. We compared the activity of WSM with that of dexamethasone on this cell line. WSM can inhibit alkaline phosphatase (ALP) activity and the activity of dexamethasone on MC3T3-E1 cells. This study shows that nacre WSM could speed up the differentiation and mineralization of this cell line more effectively than dexamethasone.