[Objectives]  There are five subtypes of serotonin receptor proteins of insects. The relationship between protein structure and the evolution of serotonin receptors in insects was comprehensively studied. [Methods]  First, the bioinformatics of 23 protein sequences of serotonin receptors in seven insects reported in the literature were analyzed; Second, the protein sequences of serotonin receptors in the NCBI database were verified by multiple sequence alignment and constructing a phylogenetic tree. [Results]  The results show that 40 of 47 putative protein sequences were those of insect serotonin receptors, whereas the other 7 protein sequences, which had 7 transmembrane regions, belong to the G protein-coupled receptor superfamily. It is uncertain if these 7 proteins are insect serotonin receptors. [Conclusion]  This study provides a basis for analyzing the function of insect serotonin receptors.