In this study, the gamma radiation absorption capabilities of some metal borides were studied by using Monte Carlo simulation method. So, the mass attenuation coefficients, mu(m), the half value layer, HVL, the tenth value layer, TVL and the mean free path, MFP values of the NdB6, SmB6 and GdB6 were calculated by means of EGSnrc particle transport code and XCOM program theoretically within the energy range 0.125-5 MeV. It was seen that there is a quite successful consistency (t = 0.00049, p = 0.99961) between the simulated results and calculated values obtained by NIST's XCOM photon cross-section database. Those computational results for the synthesized compounds have also been compared with lead and vermiculite which have concluded that NdB6, SmB6, and GdB6 arc good candidates for gamma shielding applications. These materials were sythesized by magnesiothermic reduction in open air. Stoichiometric amounts of M2O3, B2O3 and Mg (20% excess) were mixed, where M-III is a lanthanide metal (Nd-III, Sm-III and Gd-III) ion. Mixture was heated to 700 degrees C, 800 degrees C and 900 degrees C. Optimum reaction temperature and reaction time were found by X-Ray Diffraction (XRD) analysis and Scannning Electron Microscopy (SEM). By fixing the reaction temperature, reaction time has changed as 1, 2, 3, 4 and 5 h to obtain nano crystals with homogeneous morphology. It was found that optimum reaction temperature and reaction time of NdB6 is 700 degrees C and 3 h, for SmB6 700 degrees C and 1 h for GdB6 900 degrees C.