The laser ultrasonic technique was proposed to characterize the pyrolysis process of the oil shale. The ultrasonic velocity was produced by a noncontact all-optical method in the three regions of Barkol, Yaojie, and Longkou of China. It was found that the ultrasonic velocity was related with the pyrolysis temperature of the oil shale. The pyrolysis process was divided into three stages due to the ultrasonic propagation speed in the oil shale. The ultrasonic velocity had small changes from 20 to 320 degrees C in the first stage, a sharp decline between 320 and 470 degrees C in the second stage, and another small change above 470 degrees C in the third stage. The variation of the velocity was qualitatively explained, which was considered to be closely related with the characteristics of pyrolysis process in oil shale. An empirical equation of the velocity attenuation was proposed to estimate the beginning and the end of the decomposition of the kerogen. It is a new way to characterize the process of the pyrolysis of oil shale by using the laser ultrasonic technique.