Disrupting the normal signal transduction in host cells by injected bacterial effectors is a critical mechanism in bacterial pathogen-host interaction. The effectors usually harbor unique biochemical activities and function to block the anti-bacteria host defense pathways. Studies in the past few years have revealed several novel posttranslational modifications catalyzed by various bacterial effectors. The OspF family of phosphothreonine lyase effectors catalyzes "eliminylation"of phosphothreonine in MAPK, resulting permanent kinase inactivation. The NleE effector inhibits infection-induced NF-κB proinflammatory signaling by a cysteine methylation modification. The NleB effector mediates arginine GlcNAcylation of death domains and therefore blocks death receptor-mediated host cell death. The Fic-domain containing effectors VopS and IbpA transfer an AMP group onto a conserved serine or tyrosine residue in Rho GTPases, leading to Rho inactivation and disruption of the actin cytoskeleton dynamics in host cells. Identification of the biochemical activities of these effectors not only help to understand the virulence mechanism of the corresponding bacterial pathogens, but also establish a new research direction of posttranslational modifications in bacteria-host interaction studies. These effectors may also benefit or guide future study of the eukaryotic signal transduction.