When hot glass plates are quenched with cold water, several crack propagation patterns such as straight, oscillating or branching cracks, appear. In the present study, the authors examined the effect of temperature gradient on the crack propagation patterns in quenching glass plates experimentally. The temperature gradient in the glass plate is controlled by the temperature difference between the hot glass plate and the cold bath, and by descending speed into the cold bath. The experimental results show that the crack propagation pattern changes from a straight crack to an oscillating crack, then to a branching crack with increasing temperature difference and with decreasing descending speed. Also crack propagation pattern depends on plate width. Furthermore, the results shows that the crack propagation direction is strongly affected by specimen boundary.