Developing new agricultural bactericides is a feasible strategy for stopping the increase in the resistance of plant pathogenic bacteria. Some pentacyclic triterpene acid derivatives were elaborately designed and synthesized. In particular, compound A22exhibited the best antimicrobial activity againstXanthomonas oryzaepv.oryzae(Xoo) andXanthomonas axonopodispv.citri(Xac) with EC50values of 3.34 and 3.30 mg L−1, respectively. The antimicrobial mechanism showed that the compound A22induced excessive production and accumulation of reactive oxygen species (ROS) inXoocells, leading to a decrease in superoxide dismutase and catalase enzyme activities and an increase in malondialdehyde content. A22also produced increases inXoocell membrane permeability and eventual cell death. In addition, in vivo experiments showed that A22at 200 mg L−1exhibited protective activity against rice bacterial blight (50.44%) and citrus canker disease (84.37%). Therefore, this study provides a paradigm for the agricultural application of pentacyclic triterpene acid.