Insect cuticle is a fiber-reinforced composite material that consists of polysaccharide chitin fibers and a protein matrix. The molecular interactions between insect cuticle proteins and chitin that govern the assembly and evolution of cuticles are still not well understood. Herein, we report that cuticular protein hypothetical-1 (CPH-1), a newly discovered and most abundant cuticular protein from Asian corn borer , can form coacervates in the presence of chitosan. The CPH-1-chitosan coacervate microdroplets are initially liquid-like but become gel-like with increasing time or salt concentration. The liquid-to-gel transition is driven by hydrogen-bonding interactions, during which an induced β-sheet structure of CPH-1 is observed. Given the abundance of OCPH-1 in the cuticle of , this liquid-liquid phase separation process and its aging behavior could play critical roles in the formation of the cuticle.