Using a sample of 1.31 billion J/ψ events accumulated with the BESIII detector at the BEPCII collider, we report the observation of the decay J/ψ→ϕπ0, which is the first evidence for a doubly Okubo–Zweig–Iizuka suppressed electromagnetic J/ψ decay. A clear structure is observed in the K+K− mass spectrum around 1.02 GeV/c2, which can be attributed to interference between J/ψ→ϕπ0 and J/ψ→K+K−π0 decays. Due to this interference, two possible solutions are found. The corresponding measured values of the branching fraction of J/ψ→ϕπ0 are [2.94±0.16(stat)±0.16(syst)]×10−6 and [1.24±0.33(stat)±0.30(syst)]×10−7.