Abstract： Objective To investigate the effects of mineral trioxide aggregate (MTA) and calcium hydroxide on the proliferation and differentiation capacity of pulp cells of primary teeth. Methods Pulp cells were isolated from the retained primary teeth without apparent root resorption and cultured. The cells of 4-8 passages were used in the study. Cell proliferation was detected by MTr array, van Kossa staining employed to observe the formation of mineralized nodules and mRNA expression of alkaline phosphataso (ALP) and dentin sialophosphoprotein (DSPP) determined by real time PCR. Results MTA-treated cells proliferated signifieantly faster than the other two groups (F=1835.065, P < 0.01), while calcium hydroxide-treated cells grew slower than the control significantly (F=1792.301,P <0.01). The formation of mineralized nodules was found in both MTA-treated and calcium hydroxide-treated pulp cells. The number of mineralized nodules showed no significant difference between the two groups (P>0.05). Either ALP or DSPP mRNA expression showed significant difference among the three groups (F=349.651, P <0.01; F=1653.001, P<0.01). MTA increased mRNA expression of ALP and DSPP in pulp cells (P<0.01), whereas calcium hydroxide down-regnlated them (P<0.01). Conclusions MTA is more suitable than calcium hydroxide as pulp-capping agent in primary teeth.