An air cleaning and supplying system is provided to a helmet for a user riding a motorcycle. The air cleaning and supplying system is capable of providing cleaned air and supplies the same to the helmet for ventilating the air inside the helmet as well as for the motorcyclist to breathe the cleaned air when the motorcyclist is riding in a hot and air-polluted atmosphere. A blower coupled with a filter utilizes the power from the engine of the motorcycle for sucking air from the atmosphere. The filter is capable of filtering out pollutant gaseous particles from the air passing therethrough. An air hose connected between the helmet and the blower is used for conducting the cleaned air from the blower to the helmet. The cleaned air thus received by the helmet is separated into two parts: one part is sent into the helmet and used for circulating the air inside the helmet, and the other part is sent to a mouthpiece for the user to breathe.