The trend of using natural compounds or herbs containing antibacterial characteristics for disease prevention and treatment is being common, because of its environmentally friendly, and ensure food safety and animal harm reduction. There are numerous Vietnamese herbs that contain antibacterial and environmentally friendly features, however, the use of herbs in aquaculture is still limited. This study aims to determine the antibacterial components of Wedelia chinensis extract for the prevention of diseases caused by Vibrio parahaemolyticus in white-leg shrimp (Penaeus vannamei). There were 36 samples of grass (W. chinensis), which were collected in Central Vietnam and were extracted in 3 different solvents (distilled water, methanol 99.8%, and ethanol 96%) for phytochemical screening by the standard phytochemical assays. The results of the preliminary phytochemical screening in this study showed the extract in 3 different solvents containing various chemical compounds such as alkaloids, saponin, tannin, flavonoids, carbohydrates, organic acids, fixed oil, and fats. The total polyphenols and flavonoids of W. chinensis extract were analyzed by folin- ciocalteau regent (for polyphenols) and by AlCl3 (for flavonoids). The highest amount of total polyphenols and flavonoids were recorded in the W. chinensis extract in the solvent of methanol 99.8% (74.33 ± 4.49 mg GAE/g and 24.59 ± 2.19 mg RE/g dry weight, respectively), followed by in the solvent of ethanol 96% (73.65± 5.44 mg GAE/g and 20.63 ± 4.30 RE/g of dry weight respectively). The lowest of total polyphenols and flavonoids was observed in the solvent of distilled water (53.07 ± 1.48 mg GAE/g and 3.20 ± 0.07 mg RE/g, respectively). The efficiency of aqueous herbal extraction is highest in the solvent of distilled water (up to 18.2%), followed by in the solvent of ethanol 96% (11.3%), and in the solvent of methanol 99.8%, (11%). The results of antagonistic to V. parahaemolyticus testing of W. chinensis extract in 3 solvents showed that all W. chinensis extract inhibited the growth of V. parahaemolyticus, in which the diameter of the antibacterial zone of W. chinensis extracts in methanol solvent was highest up to 14.7 ± 0.91 mm. The minimum inhibitory concentrations (MIC) of W. chinensis extract in the solvents: distilled water, methanol 99.8%, and ethanol 96% against V. parahaemolyticus were 2500 mg/L, 15.5 mg/L to 15.5 mg/L, respectively. The minimum bactericidal concentration (MBC) of W. chinensis extracts was 31.25 mg/L in the solvent of methanol 99.8%, and 62.5 mg/L in the solvent of distilled water. Toxicity test of W. chinensis extract in methanol solvent 99.8% in white leg shrimp (P. vannamei) showed the concentration of 31.25 mg/L (MBC) was safe for shrimp.