The paper presents the numerical studies on spark ignition in a turbulent mixing layer formed between a fuel stream (H-2/N-2) and air flowing in the opposite directions. Compared to an ignition mechanism observed in stationary mixing layers or in premixed homogeneous mixtures studied previously by many authors, the present results show a significantly different flame formation process. At an early stage of the ignition process, the flame kernel, which is initially spherical, is strongly torn by shear stresses and vortical structures formed in a region of the mixing layer. Depending on the spark location with respect to a vortical structure three different ignition scenarios were identified: (i) the flame kernel is formed, but at the successive time instants, it is destroyed by vortices and eventually vanishes; (ii) the flame develops around the initial spark position; (iii) the flame develops being simultaneously transported along the mixing layer. In the former case the flame grows significantly faster and its volume is found to be even two times larger. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.