NO formation in premixed counter-flow flames of three syngas fuels with different compositions (0.3H(2)+0.7CO, 0.5H(2)+0.5CO, 0.7H(2)+0.3CO) were numerically investigated using the OPPDIF code over a wide strain rate range (a = 10-1000 s(-1)). The equivalence ratio was fixed at 0.5 and the USC_Mech_II mechanism coupled with NOx reaction mechanism from GRI2.11 was adopted. The strain rates of 10 s(-1) and 1000 s(-1) were selected to represent small and large strain rates. The results show that the flame temperature and maximum NO mole fraction increase first and then decrease with the increase of strain rate. At a = 10 s(-1), the flame temperature decreases with the increase of H-2 content in the syngas, and the trend is inversed at a = 1000 s(-1). Moreover, it is found that only the H-2-lean case (0.3H(2)+0.7CO) is a single flame at a = 1000 s(-1). Furthermore, the less H-2 content in the syngas, the more NO is formed at a = 10 s(-1); in contrast, more NO is observed for the syngas that contains more H-2 at a = 1000 s(-1). The reaction pathway analysis reveals that the NNH-intermediate route is the main NO formation route for all the three syngas fuels. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.