The antibiotics-resistance profiles of 28 strains of Vibrio parahaemolyticus isolated from seawater were investigated. All of the strains studied were resistant to ampicillin (100%), but susceptible to 12 other antibiotics. The minimum inhibitory concentration (MIC) of V. parahaemolyticus to ampicillin was as high as $1,024-2,048;{mu}g{cdot}mL^{-1}$. The phenotype of strain 8 changed from ampicillin-resistant to susceptible with an in-frame deletion mutant of VPA0477, a putative ${eta}$-lactamase gene, and the MIC for ampicillin of the mutant strain was $1{mu}g{cdot}mL^{-1}$. In conclusion, our findings suggest that the VPA0477 gene acts as a ${eta}$-lactamase in ampicillin-resistant V. parahaemolyticus strains.