This study investigated the neutron shielding properties of epoxy-(20B, 38.2Sm, 6.46Gd) composites in the thermal, epithermal, intermediate, and fast neutron energy regions. The neutron macroscopic cross-section, neutron attenuation ratio as a function of shield thickness (ranging from 0.05 to 10 cm), and secondary gamma rays generated by neutron interactions were calculated using the MCNP6.2 Monte Carlo simulation code. The addition of B, Sm, and Gd significantly improved the neutron shielding performance of the epoxy matrix, particularly in the thermal and epithermal energy regions. The epoxy-38.2Sm composite exhibited the highest neutron macroscopic cross-section, with a value of 44.3 cm-1 in the thermal energy region. Additionally, the most effective shielding material in the epithermal region was the epoxy-20B composite, with a macroscopic cross-section of 1.9 cm-1. Although Gd has the highest thermal neutron absorption cross-section, it is less effective than B and Sm in thermal and epithermal energy regions. The results indicate that the epoxy-20B composite provides the most effective neutron shielding properties and emits low-energy secondary gamma radiation. In addition, the linear attenuation coefficient, mass attenuation coefficient, and half-value layer values of gamma-rays in the 0.1-5 MeV energy range were calculated using the Phy-x/PSD program. Across all energy values, the epoxy-38.2Sm composite exhibited the best gamma-ray shielding performance. Future studies suggest incorporating elements with high gamma-ray absorption properties, such as tungsten, lead, or bismuth, into this composition to further reduce secondary gamma radiation.