The dielectric behavior along the ferroelectriccaxis of melt‐grown single crystals of Sr0.5Ba0.5Nb2O6has been studied under weak fields in the thermally depoled, electrically depoled, and electrically poled single‐domain condition. It is shown that the thermally depoled permittivity is high and strongly disperisve, with a marked ’’aging’’ which preferentially removes the slower relaxing components. The single‐domain permittivity is much lower, very stable, and nondispersive up to piezoelectric resonance and with low tangent &dgr;. The electrically depoled state is of even lower permittivity, and the difference from the single‐domain value is satisfactorily accounted for by clamping of the piezoelectric response. Dielectric data suggest an unusually high density of 180° walls in the thermally depoled condition, and it has not been possible to delineate the domain walls by any of the conventional methods.