Microscale gap discharge-relaxation around toner particles during triboelectrification was investigated. Single toner layers of their thickness 10-20 mu m were pinched and rubbed by two flat stainless steel electrodes between which various voltage differences were added. We found that sliding the upper electrodes enhanced successive voltage droppings between the electrodes due to gas discharge, even under 5 V of the applied potential difference which is far smaller than that allowed by Paschen's criteria in the atmospheric condition. This suggested that the electric field formed by the triboelectrified particles enhanced the inter-electrode avalanche. The measured charge amounts on the toner particles were too small to explain breakdowns with assuming traditional Paschen's criteria. For further investigation, measurement of the breakdown curve between the stainless steel electrodes was conducted. The obtained curve showed the existence gap discharge in the microscale gap range, which is out of the Paschen's criteria, and rather followed so-called modified Paschen's curve. It was suggested that discharge-relaxation between the toner and the electrodes occurred in the microscale gap region, which prevents charge accumulation in the toner layer. (C) 2014 The Society of Powder Technology Japan. Published by Elsevier B. V. and The Society of Powder Technology Japan. All rights reserved.