Bipolar electric fatigue in ferroelectric niobium-doped lead zirconate titanate stannate ceramics was investigated. Variations in the polarization and strain hysteresis loops as well as microstructural modifications of the material due to the electric cycling were analyzed. Compared with ferroelectric PZT ceramics cycled under similar conditions, the material exhibited a higher resistance to electric fatigue. Properties of the specimens showed significant decays above 106.5 cycles. Asymmetric suppression of strain hysteresis loop was monitored. At 108 cycles, the remanent polarization, the right maximum strain and the left maximum strain decreased to 70%, 58% and 44% of their initial values, respectively. The color of the material was changed from pale yellow to dark grey with cycling. The properties and color of the fatigued samples were recovered almost fully to those of the virgin state after a heat treatment at 500oC for 1 h. The pinning of domain walls, probably by oxygen vacancies, was concluded to be the predominant fatigue mechanism for the material.