Salmonella enterica serovar Gallinarum causes fowl typhoid in chickens and has been of economic importance to the chicken industry. A serovar Gallinarum live vaccine strain 9R (SG 9R) has been used to control fowl typhoid in many areas where the disease is endemic. Because the attenuation mechanism of SG 9R was not completely defined, there has been continued concern about reversion to virulence. In this study, we examined the molecular basis of attenuation of SG 9R by comparing its proteome and transcriptome with those of two wild-type strains (287/91 and 06Q110). The constantly detected spots of two wide-type strains with concomitant absence in SG 9R in two-dimensional gel electrophoresis were subjected for MALDI-TOF MS identification. Genes up- or down-regulated in SG 9R compared to wild type strains were identified using an expression array. The proteome analysis identified nine proteins absent in SG 9R. The transcriptome analysis revealed 24 up-regulated and 97 down-regulated genes in SG 9R. Approximately one-half of down-regulated genes (42 genes) were associated with virulence mechanisms. This finding suggests that attenuation of SG 9R may be associated with a large combination of impaired multiple virulence factors and reversion to virulence won’t be caused simply by any single event.