A solid solution of Sr0.5Ca0.5VOy with the perovskite structure was synthesized by a solid state chemical reaction. Sintered samples show metallic conductivity and the electrical resistivity is 1.2 x 10(-2) Omega m at room temperature. The temperature dependence of the electrical resistivity of annealed samples shows nonmetallic conductivity and at room temperature its value changes from 10(-2) to 10(1) Omega m depending on the annealing conditions; even the change in crystal data was small. This drastic change comes from slight oxidization and the carrier concentration in the conduction band may decrease on annealing. This annealing effect was also observed from magnetic susceptibility measurements.