The effect of pressure on the resistance of InS was studied to pressure higher than to 150 kbar for single crystal and to ca. 300 kbar for powdered samples. The resistance exhibits a sharp maximum at 47 kbar, which is explainable by the change of band structure due to pressure increase. Under higher pressure, the resistance decreased gradually with increasing pressure. A marked change in slope, however, was observed at 108 kbar, suggesting a phase transition possibly to a metallic phase.