A simple method to obtain calcium silicate phosphate with samarium oxide (Sm2O3) admixtures is presented. Samples were produced by mixing mineral wollastonite (CaSiO3) and Sm2O3 powders with an aqueous acidic formulation of phosphoric acid (H3PO4) at room temperature. Microstructural, mechanical, and neutron attenuation properties of phosphate pastes with Sm2O3 additions between 1 and 10 wt% were investigated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results revealed that the composites were made of remaining CaSiO3 and Sm2O3 and newly created silica (SiO2) and brushite (CaHPO4⋅2H2O) phases. The highest compressive strength (37 MPa) was achieved for phosphates pastes with 1 wt% Sm2O3 loading, representing 15% improvement over the reference sample (32 MPa). Composites with 10 wt% Sm2O3 (27 MPa) showed a reduction of 15% in compressive strength over the reference paste. Finally, the effect of Sm2O3 concentration on the neutron shielding properties was studied. For additions of 10 wt % Sm2O3 an improvement of more than 1000% in linear attenuation coefficient for thermal and epithermal neutrons was measured. Based on the overall results from this study, it is concluded that the optimum interval of Sm2O3 content in wollastonite phosphate cement for neutron shielding in nuclear systems ranged between 1 and 5 wt%.