Boron carbide/natural rubber latex (B4C/NRL) flexible films were prepared via dip-molding with B4C content in the range of 5–55 wt% for thermal neutron (0.0253 eV) shielding. B4C was well dispersed in NRL according to microscopic observation. Both the inside and outside surfaces of the film were smooth. For B4C/NRL flexible films, the minimum elongation at break was greater than 600%, the minimum tensile strength was greater than 12 MPa, and the hardness was in the range of 35–55 HA, which were suitable for preparing flexible wearable products. The attenuation efficiencies of the B4C/NRL flexible films for thermal neutrons were also calculated. The B4C/NRL flexible films exhibit good attenuation effect for thermal neutrons.