Fully hydrogenated La0.9Ce0.1Fe11.7-xMnxSi1.3 bulk hydrides with Curie temperature TC around room temperature were prepared by high-hydrogen-pressure sintering. High-resolution X-ray microtomography has been employed to analyze the morphology, size and distribution of the micropores in the sintered bulk sample. The analysis result shows that most of the micropores have the size of several micrometers with the porosity of 0.22%. A thin plate of La0.9Ce0.1Fe11.35Mn0.35Si1.3H2.0 exhibits a magnetic-entropy change ΔSm of 7.5 J/kg K at 290 K and a hysteresis loss of 0.5 J/kg for a magnetic-field change from 0 to 2 T. As the sintering pressure increases from 40 to 50 MPa, more α-Fe (~20 wt%) precipitates from the 1:13 phase, which causes a reduction of ΔSm to 6.2 J/kg K for a field change from 0 to 2 T at 297 K and a remarkable enhancement of the compressive strength from 46 to 421 MPa.