Potassium-ion batteries attract tremendous attention for large scale application due to the abundance of K resources. Herein, a highly disordered hard carbon derived from a skimmed cotton is investigated for this purpose. The study shows that a simple soaking treatment in hydrochloric acid for the skimmed cotton before its hight-emperature carbonization can critically impact the structure and the electrochemical properties of the obtained hard carbon significantly. This hard carbon exhibits a high initial coulombic efficiency (73%) and superior cycling stability and rate capability (253mAh g(-1) and 165mAh g(-1) at 40mAg(-1) and 4000mAg(-1), respectively) due to its unique porous architecture and large surface area. The full cell by coupling the hard carbon with a cathode material,i.e. potassium-rich iron hexacyanoferrate shows an outstanding electrochemical performance. These promising properties highlight the potentials of such a hard carbon in practical applications.