Low-intensity red laser light can promote cell proliferation through a wild network of signal pathways. Mammalian target of rapamycin (mTOR) pathway plays multiple roles in cell growth, proliferation, and survival. The aim of this paper is to investigate the activation of mTOR after rat bone marrow mesenchymal stem cells (MSCs) were irradiated by red light from a light-emitting diode (LED). The cells were seeded in 35mm tissue-culture dishes at a density of 8×10
cells/dish, a 96-well ELISA plate at a density of 3×10
cells/well, and cultured in Dulbecco’s modified Eagle’s medium (DMEM). BMSCs were irradiated once by 620nm red light with radiation energies 0.5 J/cm
. Methyl-tetra-zolium (MTT) assay indicated that irradiated cells significantly proliferated. This effect was confirmed by higher activity of phosphorylates mTOR. In conclusion, mTOR signal pathway may involve in red light irradiation triggered cell proliferation.