Hexagonal Co(OH)2 nanoplates with a diameter of 1.28 ± 0.08 μm and a thickness of 52 ± 14 nm were prepared, showing facile generation of static electricity in a plastic container. Based on this observation, Co(OH)2 nanoplates were incorporated into polymer matrixes such as polyvinylpyrrolidone (PVP) and polyurethane (PU). The resultant PVP–Co(OH)2 (PVP–Co) and PU–Co(OH)2 (PU–Co) films bearing an optimal amount (0.1 wt%) of Co(OH)2 nanoplates showed dramatically-enhanced triboelectric performance, compared with pristine polymer films. While PVP and PU films exhibited output peak-to-peak voltages (Vp–p) of 249 and 423 V and output peak-to-peak currents (Ip–p) of 23 and 60 μA, respectively, with a pushing force of 2 kg f, the PVP–Co0.1 and PU–Co0.1 films showed Vp–p of 407 and 612 V with Ip–p of 41 and 85 μA, respectively. Triboelectric devices fabricated with PVP–Co0.1 and PU–Co0.1 films showed the maximum power densities of 0.38 and 1.22 mW cm−2, respectively, and worked as power sources to charge a capacitor and to operate LEDs and a calculator. We suggest that the enhanced triboelectric performance of PVP–Co0.1 and PU–Co0.1 is attributable to the facile oxidation of Co2+ to Co3+ in Co(OH)2 nanoplates.