Potassium-ion batteries (PIBs) are a promising alternative to lithium-ion batteries because potassium is an abundant natural resource. To date, PIBs are in the early stages of exploration and only a few anode materials have been investigated. This study reports a cobalt sulfide and graphene (CoS@G) composite as anode electrode for PIBs for the first time. The composite features interconnect quantum dots of CoS nanoclusters uniformly anchored on graphene nanosheets. The coexistence of CoS quantum dot nanoclusters and graphene nanosheets endows the composite with large surface area, highly conductive network, robust structural stability, and excellent electrochemical energy storage performance. An unprecedented capacity of 310.8 mA h g -1 at 500 mA g -1 is obtained after 100 cycles, with a rate capability better than an equivalent sodium-ion batteries (SIBs). This work provides the evidence that PIBs can be a promising alternative to SIBs, especially at high charge-discharge rates. The development of the CoS@G anode material also provides the basis of expanding the library of suitable anode materials for PIBs.