In this study, we developed an indirect competitive plasmonic immunoassay using glucose oxidase (GOx)-induced redox reaction to etch Au nanorods (AuNRs) for qualitative and quantitative detection of aflatoxin M1 (AFM1) in milk. In this system, streptavidin (SA) was selected as a linker between biotinylated anti-AFM1-monoantibody (bio-mAb) and biotinylated GOx (bio-GOx) to form the immunocomplexes bio-mAb-SA-bio-GOx. After the oxidation of the glucose and I^-, the resultant I₂ could etch cetytrimethylammonium bromide (CTAB)-stabilized AuNRs. This resulted in the blue shift of the longitudinal localized surface plasmon resonance (LSPR) extinction peak, with a color change from blue to pink. The linear range and limit of detection (LOD) of the plasmonic immunoassay were 0.25–10 ng mL⁻¹ and 0.11 ng mL⁻¹, respectively. It displayed quantitative detection with high sensitivity, specificity, recovery, and accuracy, which is promising for qualitative and quantitative detection of AFM1 in food safety.