A series of Ca3-xLuxCo4O9+d (x = 0, 0.1, 0.2, and 0.4) has been prepared by sol-gel method. The effects of Lutetium substitution on thermoelectric properties of Ca3Co4O9+delta have been systematically investigated from 4 to 335 K. With the partial substitution of Lu3+ for Ca2+, the resistivity and thermopower for Lu-doped samples increase, while their thermal conductivity decreases. The dimensionless figure of merit for Ca2.8Lu0.2Co4O9+delta material (ZT = 0.032) is about five times better than that for Ca3Co4O9+delta (ZT = 0.007) at 335 K. Strikingly, for Lu-doped samples, the thermopower exhibits a steeper upturn at low temperatures.