Although ceramic fiber is widely used in ring liners for dental casting, its carcinogenicity is a matter of concern. We investigated the use of noncarcinogenic biosoluble fiber for ring liners. Plate-shaped biosoluble fiber was modified to obtain the same setting expansion as that of a commercial ring liner as a prototype, and we subjected it to scanning electron microscopic observation, energy-dispersive X-ray spectrometry, X-ray diffraction, and a tensile test. The main components of the prototype were Mg, Si, and O and those of the commercial sample were Al, Si, and O. The prototype and commercial samples were mostly amorphous when not heated, and crystalline components were observed after heating. The tensile strength was significantly different between the prototype and commercial samples, but the difference was small and not problematic with regard to the ring liner strength.