The present study deals with combustion and thermal transport phenomena of subsonic jet diffusion flames injected from vertical micro nozzle. Consideration is given to the flame reignition phenomenon. The hydrogen gas is employed as a fuel and its flame is visualized by the Schlieren technique and is investigated by the temperature and ion-current measurements. It is found that: (i) the small-sized flamelet (2 similar to 3 mm in diameter), which is maintained at higher temperature, appears in the vicinity of the nozzle rim, during which the reignition subsequent to the blowout of the main flame occurs, (ii) a further increase in mass flow rates makes the flamelet extinguish, resulting in no reignition, and (iii) the reignition phenomenon is ascribed to the transfer of heat and active species from the flamelet to both the hydrogen fuel jet and the surrounding air. Copyright (C) 2010 John Wiley & Sons, Ltd.