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Chitin synthase is a critical enzyme that catalyzes <i>N</i>-acetylglucosamine to form chitin, which plays an important role in the growth and development of insects. In this study, we identified a chitin synthase gene (<i>CHS</i>) with a complete open reading frame (ORF) of 3180 bp from the genome database of <i>Diaphorina citri</i>, encoding a protein of 1059 amino acid residues with the appropriate signature motifs (EDR and QRRRW). Reverse transcription-quantitative PCR (RT-qPCR) analysis suggested that <i>D. citri CHS</i> (<i>DcCHS</i>) was expressed throughout all developmental stages and all tissues. <i>DcCHS</i> had the highest expression level in the integument and fifth-instar nymph stage. Furthermore, the effects of diflubenzuron (DFB) on <i>D. citri</i> mortality and <i>DcCHS</i> expression level were investigated using fifth-instar nymph through leaf dip bioassay, and the results revealed that the nymph exposed to DFB had the highest mortality compared with control group (Triton-100). Silencing of <i>DcCHS</i> by RNA interference resulted in malformed phenotypes and increased mortality with decreased molting rate. In addition, transmission electron microscopy (TEM) and fluorescence in situ hybridization (FISH) also revealed corresponding ultrastructural defects. Our results suggest that <i>DcCHS</i> might play an important role in the development of <i>D. citri</i> and can be used as a potential target for psyllid control.