Ca0.8Y0.2-xDyxMnO3-delta (0 <= x <= 0.2) samples were fabricated by the solid-state reaction method, and their thermoelectric properties were studied from 500 degrees C to 800 degrees C. Upon the substitution of Dy3+ for Y3+ in the Ca0.8Y0.2-xDyxMnO3-delta, the electrical and thermal conductivities gradually decreased with increasing Dy3+ concentration, whereas the absolute value of the Seebeck coefficient significantly increased. The Ca0.8Y0.2-xDyxMnO3-delta showed the largest value of dimensionless figure of merit (0.180) at 800 degrees C as a result of the combination of the largest absolute value of the Seebeck coefficient and the lowest thermal conductivity. We believe that the Ca0.8Y0.2-xDyxMnO3-delta is a promising thermoelectric material at high temperatures.