It is experimentally observed that PNN-PT ceramics processed with glycerol possess superior unipolar fatigue resistance; but the same ceramics processed without glycerol are vulnerable to unipolar fatigue. For PNN-PT-glycerol fatigued by 5 x 107 unipolar cycles, there are no losses in the maximum polarization (P-max) and remnant polarization (P-r). But for PNN-PT, these losses are similar to 14% and 22%, respectively. In addition, strain asymmetry gamma(S) and internal bias field E-bias of PNN-PT-glycerol are much less than those of PNN-PT. However, the ferroelectric properties can be recovered by bipolar cycles and thermal annealing; and such recovery is much easier and larger in PNN-PT-glycerol than in PNN-PT ceramics. Scanning electron microscopy micrographs show that the significant loss in properties of the fatigued PNN-PT ceramics is accompanied by a measurable number of severely damaged grains in the samples, especially in the region near the electrode surface, whereas the much less damaged grains in the PNN-PT-glycerol ceramics contribute to their good fatigue performance.