We report the first observation of the radiative hyperonic B decay B+ -> p Lambda gamma using a 140 fb(-1) data sample recorded on the Y(4S) resonance with the Belle detector at the KEKB asymmetric energy e(+)e(-) collider. The measured branching fraction is B(B+ -> p Lambda gamma) 2:16 (+0.58)(-0:53) +/- 0:20) x 10(-6). We examine its Mp(Lambda) distribution and observe a peak near threshold. This feature is expected by the short-distance b -> s gamma transition. A search for B+ -> p Sigma(0)gamma yields no significant signal, and we set a 90% confidence level upper limit on the branching fraction of B(B+ -> p Sigma(0)gamma) < 4: 6 x 10(-6).