Aims and Objectives: The present study aims to evaluate and compare the dose enhancement factor (DEF) of tumor injected with different nanoparticles (NPs) around high dose rate (HDR) (192)Ir brachytherapy source.Materials and Methods: Monte Carlo calculations were performed with MCNPX code to determine the DEF caused by in tumor injected with (79)Au, (64)Gd, (26)Fe, and (22)Ti NPs during HDR (192)Ir brachytherapy. The uniform and non-uniform distribution of NPs within tumor was modeled with simple NPs-water mixture, and realistic nano-scale-lattice model. Furthermore, a margin of (79)Au and 64 Gd NPs was implemented around the tumor volume.Results: The increased dose caused by uniformly distributed (79)Au and 64)Gd NPs with 7, 18, and 30 mgr/gr concentrations was 4.7%, 11.8%, 19.4%, and 3.3%, 8.3%, and 18.6%, respectively. For non-uniform distribution, it was 0.4%, 1.2%, 1.9%, and 0.2%, 0.7%, and 1.2%, respectively. Increased tumor dose due to (26)Fe and 22 Ti was not significant. The peripheral-healthy tissue dose as margin with 2, 5, and 8.5 mgr/gr of 7(9)Au and 6(4)Gd increased by 1.3%, 3.6%, 6.5%, and 1.1%, 2.5%, and 4.2%, respectively. Increase the radial depth of tumor (from 1.5 to 5 cm) increase DEF (up to 22.3%). The nano-lattice model underestimated the DEF up to 4% and 3.6% for 79Au and (64)Gd NPs, respectively.Conclusion: Injecting of high-Z gold NPs into tumor increases the absorbed dose of tumor irradiated with (192)Ir HDR brachytherapy source. Size, geometry, concentration, and distribution model of NPs and tumor depth are crucial factors to accurately estimate the DEF. [ABSTRACT FROM AUTHOR]