Dual coding is a phenomenon which refers to a mature mRNA that contains two open reading frames (ORFs) in the same direction to code two different proteins. This phenomenon is quite common in prokaryote, bacteriophages and viruses as an economical and effective way to present the genome information. However, recent reports suggest that the dual coding phenomenon does also occur in eukaryote. Dual coding will help us to further understand the complicated regulation of eukaryotic genes or even the law of molecular evolution.