Nanoparticles (NPs) have been suggested to increase cancer radiotherapy efficiency. However, a fulfillment of knowledge on mechanisms of radiation dose enhancement by NPs is needed. The aim of present study was to evaluate the enhancement of radiation effects by metal NPs at physical and chemical levels. Geant4-DNA Monte Carlo simulation was used for assessment of radiation interaction processes, radiation dose effect and the produced hydrolysis byproducts following 6 MV X-rays. According to the results NPs of this study may be divided in three categories: low dose enhancers (TiO2NP, Fe3O4NP, GeNP), medium dose enhancers (BiNP, AgNP) and high dose enhancers (GNP, PtNP). It found that mass density of NPs may be the most effective feature on DER. Higher radiation enhancement efficiencies by GNP, PtNP may be produced due to the induced high energetic photoelectrons and Compton electrons and also the produced free radicals.