The effect of H2on the breakdown potential and Townsend ionization coefficients for Ne‐A mixtures were measured by the luminous‐flux method. Both argon and hydrogen form Penning mixtures with neon. The breakdown potentials for Ne‐A gas mixtures are determined by the Penning reaction, Nem+A→Ne+e+A+, between metastable neon (Nem) and ground state A atoms. At low H2concentrations (<0.1%) the breakdown potentials and Townsend ionization coefficients are unaffected. At higher H2levels (>0.1%), increase in breakdown potential caused by the lowering of the Townsend ionization coefficients depends upon the value of the product,pd, of the fill pressure ( p) and the electrode separation (d). This is due to (1) lowering of electron average energy which determines Nemdensity, and (2) nonionizing reaction, Nem+H2→H*(n=3)+H+Ne, competing with the Penning reaction between Nemand A atoms.