In this paper we describe the capability of passive millimeter-wave imaging in obstacle width and clearance measurement for automobile applications. To confirm the capabilities, a passive millimeter-wave imaging (PMMWI) test system has been developed. This test system employs the Dicke configuration, which includes a 150mm diameter antenna, a PIN switch, a reference terminator, a 50dB RF amplifier, a 76-77GHz BPF, a W-band detector, a lock-in-amplifier, an elevation and azimuth scanning stage, and a PC for scan control and data acquisition. A van and sedans are utilized as targets. The vehicle width and the clearance between two vehicles measured from PMMWIs show fairly good agreement with real values. Therefore, the capability of PMMWI in width and clearance measurement is confirmed. In addition, the experimentally obtained PMMWIs of vehicles represent the vehicle shapes. This result indicates that obstacle distinction is possible by PMMWI.