Surface contact electrification experiments have been performed on insulating polyester fibres in contact with a conductive fibre using biased atomic force microscopy tips. With positive tip bias, charge spots have been deposited in a reproducible manner. The density of deposited charges on the fibre surface was observed by Kelvin probe force microscopy as a function of time, charging position and relative humidity. Two main charge dissipation mechanisms were identified with different importance depending on the relative humidity value. Display omitted •Novel experimental setup to perform Kelvin probe force microscopy (KPFM) on individual fibres.•Electrical charges deposition on individual polyester fibres.•KPFM surface potential measurements are used to monitor the charge decay processes.•The field-adsorbed water meniscus mechanism is the main process for charging.•The dissipation mechanism depends on the relative humidity.