The genus Xanthomonas is a major group of bacterial phytopathogens with remarkable diversity and economic importance. The bacteria Xanthomonas anonopodis pv. citri (Xac) is the causal agent of the citrus canker, a serious disease that affects citrus cultivars causing serious economic impacts. After sequencing the genome of this bacterium (ONSA Network, FAPESP, Brazil), genes encoding proteins related to copper resistance (copA, copB, cutC) were identified and the involvement of the proteins in the copper resistance mechanism in Xac has been investigated. Copper compounds have been used to control plant bacterial diseases and the effectiveness of the process has been reduced by the appearance of copper-resistant bacterial strains. Here we describe the analysis of gene expression of the gene copA (1.782 bp), and copB (1.095 bp) in cells growing in the presence of copper. The expression of the genes was analyzed by Northern and Western blots. For this, cells were grown to the mid-log phase (12 h) in the absence of metal, and copper (200 mM CuSO₄.5H₂O) in a final concentration of 1 mM was added. Cell samples were removed at 0.5, 1, 2, and 4 hours after addition of copper. The total RNA and protein were extracted and gene expression was analyzed using the whole nucleotide sequences of the genes as probes (for Northern assays) or antibodies raised in rabbits against CopA and CopB proteins (for Western assays). The presence of one transcript of 2.9 kb was visualized in the Northern blot results, using either copA or copB genes as probe, showing that the genes are organized in an operon. In addition, gene transcription was specifically induced by copper but not by cadmium, silver, and zinc. The protein expression experiments confirmed the gene transcription results, the levels of CopA and CopB proteins were very low before copper addition, and the proteins were strongly induced in the presence of copper.