Heterosis-Related Gene Database (HRGD) is designed to manage the output of comparative transcriptomic studies related to heterosis (or hybrid vigor) among major agricultural crops, providing publicly available query and analysis platform for practical data mining. The database contains information concerning over 5,000 differentially expressed genes (DEGs) among the hybrid-parent tissue panels from rice genomes generated in our institute and other genomes of major cereal crops collected from published literatures. We have annotated relevant genes from manually extracted information includes not only gene sequences, genomic structures, and functional annotations but also empirical expression data generated based on various large-scale genomic methods. Tools for visualization and functional analysis of DEGs from various hybrid-parent tissue panels are also integrated via a user-friendly web interface. HRGD is a useful tool for helping plant biologists and crop breeders to explore biological knowledge that is being generated on a daily basis and in a large scale. The HRGD data resource is publicly available at http://hrgd.genomics.org.cn/.