Down syndrome (DS) is the chromosomal disorder commonly found in Thailand and worldwide. Despite the mental retardation characteristics of the patients, it has been shown that these patients also have the dental abnormalities. The behavior of cells from oral cavity in DS is still unrevealed. The aim of this study is to examine the proliferation rate and the osteogenic differentiation potential of dental pulp cells obtained from deciduous teeth from DS compared to those normal patients. MTT assay was used to examine the proliferation rate, while the RT-PCR technique was used to evaluate the level of mRNA expression of type I collagen, osteocalcin, core binding factor1 and alkaline phosphatase. Osteogenic differentiation was examined by alkaline phosphatase assay and in vitro calcification was determined by alizarin red staining. The results indicated that dental pulp cells from DS patients had slow rate of proliferation compared to cells from normal patients. However, dental pulp cells from DS patients showed high level expression of osteocalcin, core binding factor 1 and alkaline phosphatase. Moreover, increasing rate of alkaline phosphatase activity and in vitro calcification in cells from DS patients was observed. The results suggested that dental pulp cells from DS patients had slow rate of proliferation but high tendency for osteogenic differentiation compared to cells from normal patients. The knowledge may benefit the improvement of dental care and treatment for DS in the future.