A simple, rapid method for determining amoxicillin (AMO) and ampicillin (AMP) in aquatic products (flatfish, salmon, shrimp, tilapia, and yellow croaker) was evaluated. For quantification, the AMO and AMP ions at m/z 348.9 and 105.9, respectively, were selected. The limit of detection (LOD) and limit of quantification (LOQ) for detecting AMO were 0.09 and $0.25;{mu}g/L$, respectively. The respective values for AMP were 0.02 and $0.05;{mu}g/L$. After $100;{mu}g/L$ AMO treatment, the level decreased 10% after 7 days at $5^{circ}C$, while it decreased 20% at $25^{circ}C$. After 7 days, 94.9.100% of $100;{mu}g/L$ AMP remained after storage at $5^{circ}C$, while 62.3.100% remained after storage at $25^{circ}C$. Using the food code method, the recovery of AMO ranged from 64.1.92.0% and that of AMP from 44.8.86.2%. With a protein centrifugation method, the recovery of AMO ranged from 39.8.87.9% and that of AMP from 78.0.98.1%. With liquid-liquid extraction, the recovery of AMO ranged from 36.5.88.3% and that of AMP from 31.8.75.1%.