Résumé : The decay B+→ψ(2S)ϕ(1020)K+ is observed for the first time using data collected from pp collisions at s=8TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 19.6fb−1. The branching fraction of this decay is measured, using the mode B+→ψ(2S)K+ as normalization, to be (4.0±0.4(stat)±0.6(syst)±0.2(B))×10−6, where the third uncertainty is from the measured branching fraction of the normalization channel.