Title: Mimic before Reconstruct: Enhance Masked Autoencoders with Feature Mimicking. Abstract: Masked Autoencoders (MAE) have been popular paradigms for large-scale vision representation pre-training. However, MAE solely reconstructs the low-level RGB signals after the decoder and lacks supervision upon high-level semantics for the encoder, thus suffering from sub-optimal learned representations and long pre-training epochs. To alleviate this, previous methods simply replace the pixel reconstruction targets of 75% masked tokens by encoded features from pre-trained image-image (DINO) or image-language (CLIP) contrastive learning. Different from those efforts, we propose to Mimic before Reconstruct for Masked Autoencoders, named as MR-MAE, which jointly learns high-level and low-level representations without interference during pre-training. For high-level semantics, MR-MAE employs a mimic loss over 25% visible tokens from the encoder to capture the pre-trained patterns encoded in CLIP and DINO. For low-level structures, we inherit the reconstruction loss in MAE to predict RGB pixel values for 75% masked tokens after the decoder. As MR-MAE applies high-level and low-level targets respectively at different partitions, the learning conflicts between them can be naturally overcome and contribute to superior visual representations for various down-stream tasks. On ImageNet-1K, the MR-MAE base pre-trained for only 200 epochs achieves 85.0\% top-1 accuracy after fine-tuning, surpassing MAE base pre-trained for 1600 epochs by +1.4%. Furthermore, by appending masked convolution stages, MR-MCMAE reaches 85.8%, better than previous state-of-the-art BEiT V2 base by +0.3% with much fewer computational resources (25% vs 100% tokens fed in the encoder, and 400 vs 1600 pre-training epochs). Code and pre-trained models will be released.