An experimental study was conducted using outwardly propagating flame to evaluate the laminar burning velocity and flame intrinsic instability of diluted H-2/CO/air mixtures. The laminar burning velocity of H-2/CO/air mixtures diluted with CO2 and N-2 was measured at lean equivalence ratios with different dilution fractions and hydrogen fractions at 0.1 MPa; two fitting formulas are proposed to express the laminar burning velocity in our experimental scope. The flame instability was evaluated for diluted H-2/CO/air mixtures under different hydrogen fractions at 0.3 MPa and room temperature. As the H(2 )fraction in H-2/CO mixtures was more than 50%, the flame became more unstable with the decrease in equivalence ratio; however, the flame became more stable with the decrease in equivalence ratio when the hydrogen fraction was low. The flame instability of 70%H-2/30%CO premixed flames hardly changed with increasing dilution fraction. However, the flames became more stable with increasing dilution fraction for 30%H-2/70%CO premixed flames. The variation in cellular instability was analyzed, and the effects of hydrogen fraction, equivalence ratio, and dilution fraction on diffusive-thermal and hydrodynamic instabilities were discussed. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.