Objective video quality assessment (VQA) of stereoscopic three-dimensional (3-D) video plays a vital role in the application of video compression and transmission. This letter presents an efficient full-reference metric, called 3-D perceptual quality index (3-D-PQI), to measure video compression distortion of stereoscopic videos. In the metric, local video compression distortions in left and right view are measured in both spatial and temporal channels by considering contrast and motion masking effect. Then, a stereo saliency based pooling strategy is used to accumulate local spatial and temporal distortions. Finally, 3-D-PQI is derived from texture energy based fusion of distortion measurement of left and right view. A verification test of the proposed metric is conducted on publicly available stereoscopic VQA databases, which shows that 3-D-PQI is superior to other VQA metrics with respect to correlation against subjective quality judgment.