Observation of the Decay B --> Kl+l-

We report a search for the flavor-changing neutral current decay B-->K^(*)l⁺l^- using a 29.1 fb^-1 data sample accumulated at the ϒ(4S) resonance with the Belle detector at the KEKB e⁺e^- storage ring. We observe the decay process B-->Kl⁺l^-(l = e,μ), for the first time, with a branching fraction of B(B-->Kl⁺l^-) = (0.75^+0.25_-0.21+/-0.09)×10^-6.