Lactoferrin (LF) is a protein contained in milk of mammalians including human. We have already reported that LF prevented dexamethasone (DEX)-induced osteopenia in mice (Global Drugs and Therapeutics 2018). We investigated the effect of LF on decreased calcification by DEX with mouse osteoblastic cell line (MC3T3-E1), in this study. In addition, RNA expression levels of Alkaline phosphatase (ALP) and osteocalcin were measured in MC3T3-E1 cells by Real-time PCR. MC3T3-E1 cells were cultured in α-MEM containing 10%FBS. On day 4, medium was replaced by α-MEM containing 2% FBS, ascorbic acid (AA; 50µg/ml), beta-glycerophosphate (b-GP; 5mM) and DEX (3.3µg/mL) with/without LF (100µg/mL). On day11, hydroxyapatite was added into the culture medium. After 3hrs, the cells were stained with Alizarin red to evaluate calcification levels. In RT-PCR, sampling for RT-PCR was collected without exposing hydroxyapatite. In result of Alizarin red staining, decreased calcification by DEX was significantly suppressed by adding of LF. In result of RT-PCR, osteocalcin as a bone formation maker significantly decreased with exposure of DEX. The decreased osteocalcin expression level was significantly suppressed by adding of LF. These results suggested that LF suppressed reduction of calcification by DEX.