We propose a novel weakly supervised AU recognition method to learn AU classifiers with only expression labels. Specifically, we notice that there exist domain knowledge about expressions and AUs that can be represented as prior probabilities. We generate pseudo AU data for each expression; for AU classifiers’ training, we propose an RAN model, which consists of a recognition model and a discrimination mode trained simultaneously by leveraging an adversarial process, to make the distribution of the recognized AU close to the distribution of the pseudo AU data. Furthermore, we extend the proposed method to semi-supervised learning with partially AU-annotated images.