The propagation velocity of a normal zone in NbTi multi-filamentary superconducting wires has been measured in the bath temperature range of 2. 05-4. 2 K. Bare and insulated wires were utilized for the experiment in order to examine the effect of an insulation layer. For the bare wire the propagation velocity decreases gradually with decreasing temperature, then drastic reduction was observed near the lambda point, and finally no propagation occurs in pressurized He II. For the insulated wire, on the other hand, the velocity is three times larger than that for the bare wire at 4. 2 K and the propagation was observed even in He II. Numerical analysis was performed for the insulated wire. The results agree quantitatively with the experiments.