Abstract: In order to improve the efficiency of monitoring and detecting the residues of the anticoccidial veterinary drug lasalocid (LAS) in chicken, a sensitive method for the determination of LAS residues was established by surface-enhanced Raman spectroscopy (SERS). In this study, gold nanoparticles (AuNPs) with different particle sizes were first prepared, AuNPs with the optimal particle size were selected as the substrate according to SERS effect, and 4-aminophenthiophenol (PATP) was used as the probe molecule to evaluate the recurrence of AuNPs substrate. Then, by adding HNO₃, AuNPs aggregation degree was changed and LAS solubility was increased to further enhance SERS signal. Finally, the method was evaluated by establishing the standard curve and the recovery test of chicken sample. Results showed that AuNPs with a particle size of 40 nm had good enhancement effect, the SERS characteristic peak of LAS was at 1118 cm⁻¹, the AuNPs substrate had good reproducibility, and the optimal addition concentration of HNO₃ was 0.5 mol/L. The linear range of this method was 0.55×10⁻⁶~0.55 mg/mL, the detection limit was 0.23 ng/mL, the recovery rate of chicken samples was 91.9%~107.3%, and the relative standard deviation was 3.6%~5.7%, which was consistent with the detection results of the national standard method (GB31613.5-2022). This study provides a new method for the sensitive detection of LAS residues, and has reference value for the study of SERS detection method of other veterinary drug residues.