PurposeThis paper examines the short-term market impact of the beginning of the military conflict between Russia and Ukraine (February 24, 2022) on the world’s largest defense firms.Design/methodology/approachThe authors examine the world’s 100 largest listed defense firms at and around the beginning of the military conflict between Russia and Ukraine using an event-study methodology.FindingsWe observe a positive and statistically significant stock price reaction at and around the beginning of the military conflict. These results are consistent with the asset-pricing perspective/expected cash flow hypothesis. Consistent with the captured regulator theory, we find superior market returns for the two portfolios with a greater weight of defense sales. Superior market returns are also found for defense firms with higher R&D and capital expenditure intensity. Finally, these reactions are reinforced or mitigated by other firm-specific characteristics such as size, profitability and institutional ownership.Originality/valueThe effect of the war on stock markets has been relatively little examined in the financial theory. This study intends to fill this gap in the literature.