We report studies of intermittent chaos in hysteretic Josephson junctions induced by ultrashort electrical pulses. Substantial changes in the junction dc I-V characteristics, including an excessive low frequency noise, a novel re-entry state wherein the dynamics became chaotic at low dc bias, but returned to the zero-voltage state at higher biases, and a complicated behavior for very high amplitude input pulses were experimentally observed. The threshold switching curve was different from that in the static limit. The experimental findings are in good agreement with numerical simulations based on the resistively and capatively shunted junction model. © 1987 The Japan Society of Applied Physics.