The presence of silicate in artificial bone graft material is known to be effective in increasing bone formation rate. We previously reported the basic setting properties of α-tricalcium phosphate (α-Ca 3PO4; α-TCP) based apatite cement (AC) with various amount of tricalcium silicate (Ca3SiO5; alite) addition using sodium dihydrogen phosphate (NaH2PO4) as the liquid phase. In this study, in vitro biological compatibility of pure α-TCP and 2.5-10.0 wt% alite added to α-TCP based AC is investigated in terms of cell attachment, proliferation and differentiation. Set ACs aged for 168 hrs were used for cell studies with bone marrow cells from tibia of 4 week-old, male, SD rat. Initial cell attachment was observed after 7 hrs; cell proliferation was observed after 3, 5, and 7 days. Cell differentiation (alkaline phosphatase activity) was observed after 3, 6, and 9 days of incubation. Cell attachment of alite added ACs were almost the same as sintered hydroxyapatite (HAp) and alite-free AC. Cell proliferation at 2.5-7.5 wt% alite added ACs were significantly higher at day 5 and 7 (p<0.05). Alkaline phosphatase activity revealed that 2.5 wt% alite addition accelerated the osteogenic cell activity at day 6 and 9 (p<0.05) whereas too much alite addition resulted in the decrease of osteogenic cell activity. In conclusion, we found that α-TCP based AC containing appropriate amount of alite could be an improved AC since it shows suitable setting time, higher mechanical strength and possible higher osteoconductivity.