Objectives: In this study, the author aimed to evaluate the effect of BuOH fraction(YK) from Cinnamomum loureirii on osteoblast proliferation in murine rat calvarial cells. Methods: The osteoblast separated from murine calvariae was cultivated for 10 days and evaluated the cell function. After the addition of YK on the culture medium, we determined the effect of YK on the cell proliferation, alkaline phosphatase activity, apoptosis of the cultivated osteoblast, protein synthesis and collagen synthesis. Results: YK increased the proliferation of rat calvarial osteoblast. YK increased ALP activity of rat calvarial osteoblast. YK did not change the survival rate of rat calvarial osteoblast. YK increased protein synthesis of rat calvarial osteoblast. YK increased collagen synthesis of rat calvarial osteoblast. Conclusions: This study suggests that YK might improve the osteoporosis resulted from augumentation of osteoblast proliferation.