In this paper, a high-power and high-efficiency 4.3 μm mid-infrared (MIR) optical parametric oscillator (OPO) based on ZnGeP2 (ZGP) crystal is demonstrated. An acousto-optically Q-switched Ho: Y3Al5O12 laser operating at 2.1 μm with amaximum average output power of 35Wand pulse width of 38 ns at a repetition rate of 15 kHz is established and employed as the pump source. A doubly resonant OPO is designed and realized with the total MIR output power of 13.27 W, including the signal and idler output power of 2.65 W at 4.07 μm and 10.62 W at 4.3 μm. The corresponding total optical-to-optical and slope efficiencies are 37.9% and 67.1%, respectively. The shortest pulse width, beam quality factor, and output power instability are measured to be 36 ns, M2x = 1.8, M2y = 2.0, and RMS © 2022 Chinese Optics Letters.