The objective of this study is to investigate possible effects of nanometer powder of hydroxyapatite on proliferation of periodontal ligament cells. With sol-gel method, the nanometer hydroxyapatite powder were fabricated. The primary periodontal ligament cells were cultured on dense panicle hydroxyapatite and nanometer particle hydroxyapatite. The effects on proliferation of periodontal ligament cell were examined in vitro with MTT( methyl thiazolil tetracolium) test. The intercellular effects were observed with scanning electron microscopy and energy dispersive X-ray analyzer. In addition, the influence of two materials on osteogenetic differentiation was determined with measurement of ALP ( alkaline phosphatase) activity. It is concluded that nanometer hydroxyapatite can promote proliiferation and osteogenetic differentiation of periodontal ligament cells and it may become absorbable agent in osseous restoration.