The morphological transformation process of gold nanorods(Au-NRs) resulting from the reaction be-tween tetracycline and iodine was monitored by the plasmon resonance absorption(PRA) spectra and the scanning electron microscope(SEM) images.It was found that iodine could fuse Au-NRs into sphericity with the lower aspect ratio and blue shift of the longitudinal PRA band.It was found,however,that the presence of tetracycline,since it can react with I2,decreases the effective concentration of I2 and its fusion effect on Au-NRs.As a result,the longitudinal PRA of Au-NRs shifts to longer wavelength linearly with increasing the concentration of tetracycline.With that,tetracycline can be detected in the range of 5.0×105- 5.0×104 mol·L1,with a limit of determination(LOD) of 2.4×106 mol·L1(3σ).Most foreign substances in the samples did not interfere in the detection,and tetracycline in the synthetic samples could be detected with the recovery in the range of 92.8%-107.2%,and RSD lower than 4.3%.The concentration of tetracycline in milk detected with standard addition method was so low that it accorded with the safety regulation. The morphological transformation process of gold nanorods (Au-NRs) resulting from the reaction be-tween tetracycline and iodine was monitored by plasmon resonance absorption (PRA) spectra and the scanning electron microscope (SEM) images. It was found that iodine could fuse Au-NRs into sphericity with the lower aspect ratio and blue shift of the longitudinal PRA band. It was found, however, that the presence of tetracycline, since it can react with I2, decreases the effective concentration of I2 and its fusion effect on Au -NRs.As a result, the longitudinal PRA of Au-NRs shifts to longer wavelength linearly with increasing the concentration of tetracycline. Where that tetracycline can be detected in the range of 5.0 × 10 5 -5.0 × 10 4 mol·L 1 with a Limit of determination (LOD) of 2.4 × 106 mol·L1 (3σ). Host foreign substances in the samples did not interfere in the detection, and tetracycline in the synthetic samples could be detected with the recovery in the range of 92.8% -107.2 %, and RSD lower than 4.3%. The concentration of tetracycline in milk detected with standard addition method was so low that it accorded with the safety regulation.