Abstract: To evaluate the effect of quorum sensing (QS) of Aeromonas hydrophila NJ-1 on modulating pathogenic bacterial virulent factor, NJ-1 was co-cultured with Bacillus sp. R1, a AHLs degrading strain. The results showed that under monoculture conditions, the AHL amount of NJ-1 varied with the same trend as the bacteria growth curve. The maximum activity of both AHLs and virulence appeared at 27-30 h, and then decreased with the decline phase. The expression of QseB started at 27 h, and peaked at 48 h, while the expression of LuxS kept at a lower level. Under coculture conditions, AHLs bioactivity was detected only in trace level. Accordingly, the expression of LuxR was not upregulated, and the expression of virulence factors was also distinctly decreased compared to the monoculture. LuxS were upregulated at 36 h, while the expression pattern of QseB was similar to the monoculutre. In conclusion, Bacillus sp. R1 could reduce the virulence of A. hydrophila NJ-1 by the regulatition of the QS of Lux I/R through degrading AHLs activity.