Catalase is an important antioxidant enzyme that protects aerobic organisms from oxidative damage by degrading hydrogen peroxide to oxygen and water. In order to indicate the role of catalase in the thermotolerance of the western flower thrips, Frankliniella occidentalis (Pergande), a major pest of agricultural and horticultural crops, we cloned the cDNA encoding catalase from F. occidentalis in this study. Sequence analyses indicated that the catalase gene from F. occidentalis (FoCAT) encoded a protein containing 506 amino acids, including three catalytic amino acid residues (His-73, Asn-146, and Tyr-356), the proximal heme-ligand signature sequence, ⁶²FDRERIQERVVHAKGAG⁷⁸, and the proximal active site, ³⁵²RIFSYADTH³⁶⁰. Phylogenetic analysis indicated that CAT from different insect species could be grouped into a well-supported cluster that included Diptera, Lepidoptera, and Hemiptera. qRT-PCR analyses initially indicated that FoCAT expression was significantly up-regulated under heat and cold stress. When F. occidentalis nymphs were incubated at 37 or – 6 ° C, FoCAT expression showed a significant increase at 2 h for both temperatures and then declined when the temperature duration was 4 or 8 h. The enzymatic activity of FoCAT was significantly elevated at moderate heat stress (33 ° C), but showed a significant decrease at – 6 ° C. When F. occidentalis nymphs were incubated at 37 or – 6 ° C, FoCAT activity showed a gradual decline for both temperatures and was lowest at the 8-h exposure time. In conclusion, FoCAT plays an important role in the thermotolerance of F. occidentalis, which may partially explain the widespread distribution of this important pest.