As the developed investments material, Gypsum-bonded Investments have been used for Dental Castings, especially Gold-Alloys. Investments for Casting have Calcium sulfate hemihydrate as binders and Quartz or Cristobalite as Refractory Fillers. In this case, The rate of thermal expansion must be higher thermal expansion as compensating for Gold-alloy`s contraction during solidification. In this study, We have made the effects on Setting and Thermal expansion of investments including cristobalite, mullite and chamotte as a refractory. Setting expansion was changed with the content of water and absorption property of surface on refractory fillers. Thermal expansion was presented to drop of expansion by diffenrence of the rate of thermal expansion on Refractory fillers. (Received December 19, 1998)