The hydrophobic nature of thymoquinone (TQ) compromises its bioavailability and limits its effectiveness as an anticancer compound. The preparation and evaluation of TQ-microemulsion formulations was investigated. Parenteral and oral formulations of TQ-microemulsions were prepared by studying the solubility of TQ in different oils, surfactants and co-surfactants and investigating their stability, globule size, zeta potential, and in vitro and in vivo activity by scintigraphic evaluation of the technetium-99m-radiolabelled TQ-microemulsions. The mean globule size of the TQ-micremulsions was on the nanometer scale. The mean size of the oral formulation remained constant in distilled water and in buffers of various pH for 6 h, while the parenteral formulation was found to be stable for 72 h in distilled water and various aqueous solutions. The in vitro anticancer activity of the TQ formulations against MCF7 and Wehi 164 cell lines was evaluated and determined to be superior to plain TQ. Relative tumor volumes (RTV) of mice transplanted with MCF cells after oral and intravenous administration of TQ-microemulsions were measured to be 6 and 73.2 mm3 respectively compared to 21.1 nd 231 mm3 for administration of plain TQ. Similarly, mice transplanted with murine fibrosarcoma cells had RTVs of 68 and 175.3 mm3 after oral and parenteral administration of TQ-microemulsions compared to 190.1 and 214 mm3 for analogous administration of plain TQ. Our study is the first to describe the preparation, scintigraphic evaluation and biodistribution of TQ-microemulsion formulations. The superior properties of the microemulsion formulations potentiate their future use in the treatment of solid tumors.