The study of hydrogen isotopes in fluid inclusions is of great significance in the evolution of ore deposits, speleothem research and fluid migration. Conventional analysis methods are based on off-line thermal decrepitation or mechanical crushing followed by dual-inlet isotope ratio mass spectrometry (DI-IRMS). Because a large sample size (at least 1?g) is required for the conventional methods, the hydrogen isotope analysis of small-sized quartz samples is challenging.,A method for the hydrogen isotope analysis of H2 O from fluid inclusions in minerals using a Cr-EA/IRMS method (a single-oven, chromium-filled elemental analyzer coupled to IRMS) is presented. The reactor is filled with chromium reagent instead of glassy carbon chips, which allows quantitative conversion of the H2 O in quartz inclusions into H2 for the first time. The hydrogen isotope ratio is then determined by continuous-flow IRMS.,Eight quartz samples were analyzed using the Cr-EA/IRMS method. The hydrogen isotope ratios obtained using this method were consistent with those obtained using the off-line method. For small samples of less than 20?mg, the δ2 H values showed large variance (6-15‰), suggesting that the results were significantly influenced by the background. In contrast, the reproducibility of the δ2 H values for samples of more than 20?mg was better than 3‰.,The proposed Cr-EA/IRMS method greatly reduces the minimum sample size (to ca 20?mg) and the laboratory time (30 samples each day) without compromising precision compared with the off-line method. The method offers a reliable and economic approach for measuring the δ2 H values of geological samples.,? 2019 John Wiley & Sons, Ltd.