Mechanical, microstructural and neutron attenuation properties of white ordinary Portland cement (WOPC) pastes with Sm2O3 additions ranging from 2.5 to 20 wt% are reported. Scanning electron microscopy (SEM) micrographs revealed that incorporation of Sm2O3 above 10 wt% enhance the formation of ettringite and increase the porosity of the cement composites. Microcracks were also observed in SEM images for compositions containing 20 wt% Sm2O3. X-ray diffraction (XRD) analysis determined that samarium oxide particles did not interact chemically with the cement matrix to form new crystalline phases. On the other hand, neutron transmission experiments and Monte Carlo simulations showed that the attenuation of thermal and epithermal neutrons increased significantly with the addition of Sm2O3. Maximum enhancement in neutron shielding was obtained for specimens loaded with 20 wt% Sm2O3, which have an effective removal cross section of Σeff=4.018cm-1 compared to Σeff=0.515cm-1 for plain WOPC paste.