A high second harmonic generation response is demonstrated by a Pb6O5(NO3)(2) lead oxynitrate whose identity was verified upon reinvestigation of the PbO-Pb(NO3)(2) system. Its crystal structure exhibits a unique cationic [Pb6O5](2+) framework hosting orientationally ordered NO3- triangles in the channels. Easy preparation and high thermal stability (until similar to 500 degrees C in air) suggest it to be a new promising NLO material.