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Designing highly active and durable catalysts is considered to be crucial for enhancing hydrogen evolution reaction (HER) from water electrolysis. Although some studies indicate that anatase TiO 2 is a promising candidate for electrolytic hydrogen evolution reaction, the influence of different crystalline phases of TiO 2 on the supported Ru catalysts for electrocatalytic HER performance is rarely systematically explored. Herein, a series of Ru/TiO 2 -X (X = R (Rutile), A (Anatase), and P25) catalysts were prepared to investigate the influence of the rutile and anatase phases of TiO 2 on the catalytic activity of Ru catalysts in HER. The findings demonstrate that the HER activity is much affected by the variation of the titania structure, when other factors are kept constant. The 15Ru/TiO 2 -R-H 2 has superior HER performance with a small overpotential of 63 mV to achieve a current density of 10 mA cm−2 in acidic electrolyte and 99 mV in alkaline electrolyte compared to 15Ru/TiO 2 -A-H 2 and 15Ru/TiO 2 -P25-H 2. This might be attributed to the faster electron transfer and lower Fermi level caused by the oxygen vacancy (V O) and strong metal-support interaction (SMSI), along with the exposure of active sites afforded by the highly dispersed ruthenium nanoparticles on the rutile TiO 2. Our results indicate that the presence of rutile TiO 2 support alone is adequate to maintain Ru in its most active form and make it a more performing catalyst, compared to anatase titania and P25. • Ru is supported on different crystalline phase of TiO 2 for electrocatalytic HER. • Partial Ru is incorporated the lattice of TiO 2 -R with SMSI effect. • Highly dispersed Ru and rich V O promote electrocatalytic HER. • Electron transfer from V O and Ti to surface Ru is conducive to optimizing HER. [ABSTRACT FROM AUTHOR]