The genus Xanthomonas is composed of several species that cause severe crop losses around the world. In Latin America, one of the most relevant species is Xanthomonas campestris pv. campestris, which is responsible for black rot in cruciferous plants. This pathogen causes yield losses in several cultures, including cabbage, cauliflower and broccoli. Although the complete structural genome of X. campestris pv. campestris has been elucidated, little is known about the protein expression of this pathogen in close interaction with the host plant. Recently, a method for in vivo analysis of Xanthomonas axonopodis pv. citri was developed. In the present study, this technique was employed for the characterization of the protein expression of X. campestris pv. campestris in close interaction with the host plant Brassica oleracea. The bacterium was infiltrated into leaves of the susceptible cultivar and later recovered for proteome analysis. Recovered cells were used for protein extraction and separated by two-dimensional electrophoresis. Proteins were analysed by peptide mass fingerprinting or de novo sequencing and identified by searches in public databases. The approach used in this study may be extremely useful in further analyses in order to develop novel strategies to control this important plant pathogen.