The study aimed to determine extract yield (%), antibacterial activity, and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of plant extracts from dried and fresh herbal plants (Phyllanthus amarus) against Vibrio parahaemolyticus strain causing acute hepatopancreatic necrosis disease (AHPND) in white leg shrimp (L. vannamei). The result showed that the extract yields of dry and fresh herbs reached 11.50% and 2.75%, respectively and the antibacterial activity of the two extracts both are good at concentrations from 250 to 1,000 mg/mL at the same bacterial density of 10⁶ CFU/mL. Specifically, the diameter of the inhibition zone at 250; 500; 750 and 1,000 mg/mL concentration of dried herbal extracts reached 16.75±0.96; 18.50±1.29; 20.75±0.96 and 21.25±0.50 mm, while that of fresh herbal extracts reached 14.50±1.29; 16.25±0.50; 16.75±0.50 and 17.00±0.00 mm, respectively, with a statistically significant difference p<0.05. The result also showed that MIC values of dried and fresh extracts were defined at 125 mg/mL and 250 mg/mL, respectively and that MBC values of the extracts were 500 and 1,000 mg/mL respectively. The GC-MS analysis revealed that there were 19 natural compounds in the dried extract, in which Ethyl Linoleolate (C₂₀H₃₆O₂) compound occupied the highest ratio (22.43 %), while 2.3-Dihydro-3.5-dihydroxy-6-methy-4H-pyran-4-one (C₆H₈O₄) was the lowest (0.24 %).