The recent attention to energy-saving housing has increased demand for high-performance heat insulators. Among several heat insulators, inorganic fibrous heat-insulators have various merits, but production costs are still high. This work proposes a fabrication process of water glass fibers by centrifugal spinning using a concentrated aqueous solution of sodium silicate as spinning solution. It was found that fiber thickness and distribution are strongly affected by the process parameters, and that larger centrifugal gravity provides thinner and more uniform fibers. In contrast, the viscosity of spinning solution scarcely affected the thickness and uniformity of fibers, and a spinning solution with viscosity of more than 3 Pa.s and less than 150 Pa.s gave fibers stably. Humidity-resistant fibers were produced by carbon dioxide gas treatment at over 100 degrees C. Thermal conductivity measurement revealed that the optimal value was 0.027W/(m.K), which is comparable to that of air in the absence of convection. This value was similar to that of commercially available glass wool, but the mass of fiber required was about one-half, which would be effective for cost reduction.