Applications of 1-alkyl-3-methylimidazolium salts ([amim]X) in pharmaceuticals call for studies on the biological effects. Previously, [amim]Cl and [amim]Br caused time-dependent stimulatory effects on Vibrio qinghaiensis sp.-Q67 (Q67). Further studies are still needed to answer the question whether [amim]X with other anions have similar effects, and to explain such stimulatory effects. Here, effects of four [amim]BF4 with different alkyl side chains on Q67 were investigated. At the apical level, they inhibited luminescence at high concentrations and the toxicities decreased with time increasing from 0.25 to 12 h. Meanwhile, they Stimulated luminescence at low concentrations, and the stimulations increased over time. The maximum stimulations followed an order of [emim]BF4 > [bmim]BF4 > [hmim]BF4 > [omim]BF4. Compared with [emim]BF4, imidazole caused lower stimulations, while NaBF4 caused significantly higher ones. Overview on effects of [amim]BF4, imidazole and NaBF4 indicated significant anionic contributions. At biochemical and molecular levels, favin mono-nucleotide (FMN) and nicotinamide adenine dinucleotide (NADH) increased over time, and expressions of luxA and luxB (encoding luciferase that catalyzes FMN:NADH reaction) in Q67 showed up-regulations, suggesting an overall enhancement of the bioactivities. Moreover, superoxide dismutase and catalase showed inductions with up-regulations on their encoding genes, indicating improved antioxidant responses. (C) 2015 Elsevier B.V. All rights reserved.