We report on the structural, electrical, and thermal transport properties of the single crystals of Bi2Sr2Co2-x Ir (x) O (y) (0 a parts per thousand currency sign x a parts per thousand currency sign 0.2). Large-sized (centimeter-level) and good-quality single crystals were grown by a modified flux method. The substitution of Ir ions for Co ones makes the in-plane resistivity rho (ab) increase monotonically, whereas, the in-plane thermopower S (ab) initially increases and then decreases as x is larger than 0.1. Therefore, among all samples, the in-plane power factor P (ab) (=S (ab) (2) /rho (ab)) of Bi2Sr2Co1.9Ir0.1O (y) would reach a maximum value of 116.4 mu Wm(-1)K(-2) at 300 K and shows a significant improvement of about 20 % compared to that of the parent sample. Our results indicate that an appropriate doping of Ir ions at Co-sites may provide an effective way to enhance the thermoelectric performance of Bi2Sr2Co2O (y) system.