Passively Q-switched laser operation with Yb:GdCOB crystal is demonstrated in a plano-concave resonator, utilizing a Cr4+:YAG saturable absorber. When the absorbed pump power of the 2-mm thick X-cut crystal is 6.3 W, an average pulsed output power of 0.62 W, with polarization parallel to the Z principal axis, is generated at a pulse repetition frequency of 3.6 kHz. The resulting pulse energy, duration, and peak power are 172 μJ, 20 ns, and 8.6 kW, respectively.