Zn is an essential cofactor for enzymes involved in the synthesis of various bone matrix constituents, thus it stimulates bone mineralization in vivo and in vitro. We determined whether zinc would affect extracellular matrix mineralization and bone-related gene and transcription factor Runx2 expression. Leptin receptor gene expression was also measured, since leptin is thought to be a negative effector for bone formation, although this is still controversial. Osteoblastic MC3T3-E1 cells were cultured at 0 to 15 µM ZnCl2 (Zn- or Zn+) at different time intervals. Extracellular matrix mineralization was detected by staining for calcium deposits using Alizarin Red and von Kossa stains, and for alkaline phosphatase using ALP stain. Extracellular matrix mineralization and ALPstain were increased in the zinc conc- and time-dependent manners. Bone-related proteins (ALP, osteocalcin, osteopontin and PTH receptor) and Runx2 gene expressions were also increased by conc- and time-dependent manners. Results indicated that zinc increased extracellular matrix mineralization, bone-related gene and Runx2 expression in osteoblastic MC3T3-E1 cells. The study results also promote further study of the interaction between zinc and leptin in bone formation.