This work reports the first demonstration of bismuth oxyhalides as anode materials in potassium-ion batteries. BiOCl nanoflake assemblies deliver high capacities of 367 mA h g-1 at 50 mA g-1 and 175 mA h g-1 at 1 A g-1. The formation of K-Bi alloys at an early stage of potassiation is observed.