Abstract: In order to establish a rapid screening method for chlorothalonil residues in blueberry samples, the pesticide chlorothalonil was used as the target analyte in this study, and the effects of colloidal gold labeling parameters and sample preparation methods on colloidal gold immuno-chromatographic assay (GICA) were systematically studied. Firstly, 25 nm colloidal gold nanoparticles labelled with anti-chlorothalonil monoclonal antibody was used as the detection probe. Chlorothalonil-BSA (1 mg/mL) conjugate and goat anti-mouse IgG antibody (0.1 mg/mL) were coated on nitrocellulose filter membrane (NC) to form the test line (T) and quality control line (C), respectively. Then the blueberry samples were extracted with acidic acetonitrile and diluted with double distilled water (dd H₂O), and were detected by the assembled immuno-chromatographic test strip. The qualitative and semi-quantitative analysis of chlorothalonil in blueberries could be accomplished within 15 minutes, and the limit of detection (LOD) observed by naked eyes was 0.1 mg/kg. The cross-reactivity for the detection of 4-hydroxy-chlorothalonil, quintozene, carbendazim and procymidone was negligible. The recovery results of chlorothalonil in blueberry using the colloidal gold immuno-chromatographic test strip were consistent with those of the UPLC-MS/MS method. Both methods could be successfully applied to the detection of chlorothalonil in blueberries. The immuno-chromatographic test strip is helpful for on-site detection, while the UPLC-MS /MS method can provide accurate quantification.