A vehicular sensor mounting structure for a sensor that is mounted on a roof of a vehicle to detect an environment outside the vehicle is equipped with a bracket attached to the roof to support the sensor in a swingable manner, and a cover member having a sensor opening portion that opens toward an outer periphery of the vehicle, and provided on the roof in such a manner as to cover the sensor from above. The cover member has a wire harness cover portion covering, from above, a wire harness that passes through the roof from below, that protrudes into the cover member, and that is connected to the sensor.