Abstract: A terahertz (THz) imaging system based on a backward-wave oscillator (BWO) is presented. BWO continuous THz wave imaging is a new approach to nondestructive testing. In the experiment, a sample was scanned on an X-Z 2-D translation stage, and the THz intensity information of the sample was picked up by a pyroelectric detector for imaging with a computer. A number of potential imaging applications were demonstrated by using the 0.71THz radiation, including nondestructive real-time testing of fare cards for bus passengers, Campus IC Card and coins in an envelop. The current setup is capable of resolving an object of 1.5mm size. It is concluded that a BWO THz imaging system is very practical and effective tool in nondestructive identification and security inspection.