Abstract: The inhibitory effects of 31 traditional Chinese herbal medicines on 6 pathogenic bacteria of seawater-cultured animals in vitro were studied with the diffusion method and decuple dilution method, respectively. The results showed that Psidium guajava, Atractylodes lancea, Scutellaria and Eugenia caryophyllata were the most effective medicines for inhibiting the growth of Photobacterium damselae subsp. piscicida among the tested; Cinnamomum cassia and Polygonum chinense were the effective medicines for inhibiting Vibrio parahemolyticus. Then, Lsatis tinctoria, Ligustrum lucidum and Atractylodes macrocephala affected the bacteria to some extent, and the others were non-effective (or could inhibit the bacteria lightly only at a high concentration).Conversely, homo-bacterium had different sensitiveness to different medicines, but only a few effective medicines could be screened out, so the medicine screening is very important for Chinese herbal medicine uses. It also showed that decuple dilution in test tubes method was more compatible than the diffusion on the plate method for effective medicine screening. Moreover, Chinese herbal powder was more effective than the water extracts at the same concentration according to the results from decuple dilution in test tubes method.