Aim: To demonstrate the influence of copper on luminescence and toxin production in Vibrio harveyi. Methods and Results: The effect of copper concentration on the expression of both luminescence and toxin of V. harveyi was investigated. Copper concentration of less than 40 ppm had no effect on the growth. While V. harveyi cultured with 40 ppm copper concentration showed decreased luminescence as measured by spectrofluorophotometer and as observed. LuxD gene, which is related to luminescence expression, was monitored using real-time RT-PCR. Result showed that the concentration of cDNA coding for luxD was lower in V. harveyi with copper. Toxic activity against both HeLa cells and shrimp haemocytes was also lower in the culture supernatant of V. harveyi grown with 40 ppm copper concentration. Moreover, V. harveyi extracellular proteins were analysed using SDS-PAGE. Results showed that culture supernatant from V. harveyi grown without copper had thicker band indicating a higher concentration of the putative cysteine protease, one of the major toxin of V. harveyi. Conclusions: This study proved that both luminescence and toxin were repressed by copper. Significance and Impact of the Study: The current study demonstrated that copper inhibited expression of phenotype of V. harveyi. Furthermore, it may inhibit quorum sensing of V. harveyi.