Low level laser therapy (LLLT) affects various biological processes, and it is said that the non-coherent light of the light-emitting diode (LED) has a similar action. The purpose of this study was to examine the effects of LED light on the proliferation and differentiation of osteoblasts-like MC3T3-E1 cells cultured in osteogenic differentiation medium (ODM) over the long term. Cells were irradiated with red LED light of 630 nm at three doses; 0.5J/cm², 1.5J/cm² or 3.0J/cm² for the cell proliferation activity assay, and at 0.5J/cm² for the osteogenic differentiation activity assay. The former activity was checked by counting the number of viable cells using Trypan blue dye. The latter activity was evaluated by alkaline phosphatase (ALP) staining and examining the mRNA expression of the osteopontin (OPN) gene using real-time quantitative PCR. The number of viable MC3T3-E1 cells showed a tendency to increase after the irradiation at all three energy densities in comparison with a non-irradiation group (control group). In particular, there was a remarkable 3.34-fold increase in the group irradiated with 3.0J/cm² on day 7 after starting the culture. On culture day 15, there was a tendency for the red LED irradiation group (0.5 J/cm²) to exhibit more staining for ALP than the control group, and the expression of OPN was significantly higher in the irradiation group on culture day 16. In conclusion, low level red LED light can enhance MC3T3-E1 cell proliferation and osteogenic differentiation when the cells are cultured for a relatively long time.