Photobiomodulation (PBM) triggers proliferation of many type of cell, including fibroblasts. Although PBM has positive effects on modulation of ample biological processes, significant contradictions in underlying process has been waiting for gathering and clarifying. This preliminary study evaluated the efficacy of correct combination between different energy densities and intensities of 635 nm laser light. This study aimed to investigate and identify the compatible match of energy and power density to proliferate L929 cell line. Cells were plated at a cell density of 20,000cells per well on 96-well polystyrene plates. The plates were incubated for 24 h and then, the wells were irradiated using power densities of 30 mW/cm2, 50 mW/cm2, 125 mW/cm2, and 200 mW/cm2. Energy densities used in this study were 1 J/cm2, 3 J/cm2, and 5 J/cm2. 1 J/cm2 laser energy density stimulated significantly the proliferation of L929 cells at 30 mW/cm2, 50 mW/cm2, 125 mW/cm2. However, the proliferation at 3 J/cm2 was significantly (p ≤ 0.05) higher than the proliferation at 1 J/cm2 when 200 mW/cm2 of laser power density was used. In conclusion, the results show that the stimulatory effect of PBM depends on both energy density and power density. Thus, the combination of laser energy density and intensity may change the treatment response.