Antioxidants are substances that function to protect cells from damage caused by unstable free radicals and reactive oxygen species (ROS). These agents are also quite successful in deterring certain disease processes specifically, cancer. Antioxidants help fight these excess free radicals or ROS by donating electrons to make a more stable chemical group. Thymoquinone (TQ) is a major active component of black seed (Nigella sativa) and has been used in the Middle East for centuries to treat disease processes. Selenium (Se), unlike TQ, is found in almost all human tissue and is classified as a trace element. Se has the ability to modify cells by acting as antioxidants, modifying redox status and thyroid hormone metabolism. The purpose of this study was to further examine the use of TQ, an extra-cellular anti-oxidant, and Se, an endogenous antioxidant on the proliferation of osteoblasts cells (MG 63) in tissue culture. MG 63 cells were treated with conventional low, medium and high doses of TQ and Se to obtain an optimal dose for combined treatment. Results and biochemical markers were evaluated at 24, 48 and 72 hours for all groups. The combined dose of TQ and Se produced decreased cell counts, increased cellular damage, decreased alkaline phosphatase levels, and decreased glutathione levels as compared to control (P>0.05). These results indicate that the combined use of TQ and Se may be an effective treatment option against human osteosarcoma cells.