Effects of one-quantum excitation of the antisymmetric-stretching mode of CH4(v3 = 1) on the O(3P) + CH4 reaction were studied in a crossed-beam, ion-imaging experiment. In the post-threshold region, we found that (1) the product state distributions are dominated by the CH3(00) + OH(v′ = 1) pair, (2) the product angular distributions extend toward sideways from the backward dominance of the ground-state reaction, and (3) vibrational excitation exerts a positive effect on reactivity, but translational energy is more efficient in promoting the rate of this central-barrier reaction. All major findings agree reasonably well with recent theoretical results. Some remaining questions are pointed out.