The experimental study of flammability limits of counterflow premixed methane-air flames in a planar micro channel is described in the paper. Combustion occurs in the gap between quartz plates which are connected with two countercurrent slot burners. The proposed counterflow burner allows investigation of the flame structure at low flow rates which are outside the applicability range of conventional counterflow burners at the normal gravity conditions. It was found that the heat return from combustion products to unburned mixture through the heat conducting plates is an essential effect at low gas flow rates. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.