Five types of Ca2SiO4 solid solutions, doped with either P5+, Ge4+, Fe3+, Mg2+, or Ba2+, were prepared and examined by high-temperature X-ray diffractometry up to 800degreesC. The starting and finishing temperatures were determined for the alpha(L)'-to-beta martensitic transformation during cooling and the reverse (beta-to-alpha(L)') transformation during heating. These four types of transformation temperatures for the preparations doped with either P5+ or Ge4+ steadily decreased with increasing substituted fraction. The effect of the substitution on the decrease for each transformation temperature was quantitatively evaluated by DeltaT/x, where DeltaT is the difference in the transformation temperatures between the solid solutions and pure Ca2SiO4, and x represents the fraction substituted for Si4+ or Ca2+ in the alpha(L)'-phase structure. The evaluated value for the substitution of P5+ was more than 3 times that of Ge4+. The effect of the substituent ions mentioned above, together with Na+ and Sr2+, on the lowering of the starting temperature of the alpha(L)'-to-beta transformation was principally determined by the differences in the ionic radius between the interchanging cations.