Electrically induced fatigue crack growth is an important degradation mechanism for ferroelectric devices. Reliability concerns for ferroelectric devices place stringent demands for ferroelectric materials. In situ observation of electrically induced fatigue crack growth was carried out for ferroelectric single crystals under alternating electric field. Electrically induced fatigue crack growth was observed both below and above the coercive field. Crack closure and open behavior were observed together with 90 degrees ferroelectric domain switching during the electric cycling. The crack propagation behavior is a repeated process of continuous but small increments followed by a sudden increase in the crack length. It was suggested that the electric boundary condition along the crack face, from its mouth to its tip, is a variation from the impermeable to the permeable state. The gradual attainment of an impermeable crack tip after an incubation period of field cycling causes the observed jump in crack propagation.