Summary Thiazole, isothiazole, thiadiazole, and their derivatives are used to control various human, animal and plant diseases. In addition to having direct anti‐microbial and anti‐fungal properties, these compounds are thought to induce host defences, but the mechanism of defence induction remains poorly understood. This article reports that the thiadiazoles of zinc thiazole and bismerthiazol induce H 2 O 2 accumulation, up‐regulation of defence‐related genes, callose deposition and hypersensitive response‐like cell death in rice leaves infected with X anthomonas oryaze pv. oryzae ( Xoo ) strain ZJ 173, but not in non‐infected leaves. These defence responses in Xoo ‐infected leaves were suppressed by the exogenous application of catalase, which reduces H 2 O 2 accumulation. The application of extracellular polysaccharides ( EPS s) extracted from strain ZJ 173 significantly compromised rice defence against ZJ 173 with or without thiadiazole treatment. The EPS ‐deficient Xoo mutant ∆ gumH triggered a stronger defence than its parent strain ZJ 173. The thiadiazole treatments reduced EPS production by strain ZJ 173, but not by the thiadiazole‐resistant strain 2‐1‐1, which is thiadiazole resistant in vivo , but not in vitro ; moreover, enhanced defence was not detected in thiadiazole‐treated rice inoculated with 2‐1‐1. Based on these data, we infer that zinc thiazole and bismerthiazol promote rice defence against Xoo by inhibiting the production of bacterial EPS .