Aims: Developing new bio-agents to control plant disease is desirable. Entomopathogenic bacteria Xenorhabdus spp. have potential antimicrobial activity in agriculture. This work was conducted to evaluate the antimicrobial activity of Xenorhabdus bovienii YL002 on plant pathogenic fungi and oomycete in vitro and the efficiency of this strain to reduce the in vivo incidence of grey mould rot on tomato plants caused by Botrytis cinerea and leaf scorch on pepper plants caused by Phytophthora capsici. Methods and Results: The antimicrobial activity of X. bovienii YL002 was firstly determined on in vitro plant pathogenic fungi and oomycete and then on tomato fruits and plants infected with B. cinerea and pepper plants infected with P. capsici. The cell-free filtrate of X. bovienii YL002 exhibited highest inhibition effects (>98%) on mycelia growth of P. capsici and B. cinerea. The 50% inhibition concentration (EC(50)) of the methanol-extracted bioactive compounds (methanol extract) of the cell-free filtrate against P. capsici and B. cinerea were 164 83 and 42 16 mu g ml(-1). The methanol extract also had a strong effect on the spore germination of P. capsici and B. cinerea, with a EC(50) of 70 38 and 69 33 mu g ml(-1), respectively. At 1000 mu g ml(-1), the methanol extract showed a therapeutic effect of 70.82% and a protective effect of 77.4% against B. cinerea on tomato plants compared with the control. The methanol extract also showed potent effect against P. capsici, with a therapeutic effect of 68.14% and a protective effect of 65.46% on pepper plants compared with the control. Conclusions: Xenorhabdus bovienii YL002 produces antimicrobial compounds with strong activity on plant pathogenic fungi and oomycete and has the potential for controlling grey mould rot of tomato plants and leaf scorch of pepper and could be useful in integrated control against diverse plant pathogenic fungi and oomycete. Significance and Impact of the Study: This study showed the potential that X. bovienii YL002 can be used to control the grey mould rot caused by B. cinerea on tomato plants and leaf scorch caused by P. capsici on pepper plants with the objective to reduce treatments with chemical fungicides.