Title: Representation Mutual Learning for End-to-End Weakly-Supervised Semantic Segmentation. Abstract: In recent years, end-to-end solutions for Weakly Supervised Semantic Segmentation (WSSS) with image-level labels have been developed rapidly. Previous end-to-end methods usually rely on segmentation branches or decoders to predict segmentation masks, bringing additional parameter numbers and consumption time. In this paper, we propose a decoder-free Representation Mutual Learning (RML) framework to directly predict segmentation masks, which leverages collaborative learning and mutual teaching among multi-level feature representations to improve segmentation performance. Our RML is a straightforward and efficient end-to-end WSSS framework, which incorporates the instance-level, feature-level and pixel-level representation mutual learning strategies to improve segmentation quality. To enhance the Class Activation Map (CAM) representations, we propose a CAM-driven Instance-leave Mutual Learning strategy that preserves the equivariance of CAMs and expands the distance between different classes of semantic prototypes. Besides, we design a Multi-scale Feature-leave Mutual Learning strategy, which can align aggregated contextual representations and facilitate the representation capability of contextual representations. Furthermore, we also provide an Affinity-aware Pixel-level Mutual Learning strategy to learn semantic affinity representations. Experiments validate that our RML yields a significant performance improvement over recent end-to-end methods on the Pascal VOC 2012 dataset and the MS COCO 2014 dataset. The release code is available at supplementary material.