Developing alternatives to platinum-based electrocatalysts for the hydrogen evolution reaction (HER) is an important challenge for realizing the green transition. This is especially the case for alkaline conditions where Pt-based catalysts have very poor stability. Here, we demonstrate a new solvothermal synthesis method with facile allotropism control for selectively obtaining hexagonal-close-packed (hcp) and face-centered cubic (fcc) ruthenium nanoparticles. Both samples are highly active and durable HER catalysts in alkaline conditions outperforming state-of-the-art Pt/C. However, the samples show markedly different stabilities. The hcp sample shows exceptional stability for 12 hours constant operation at 10 mA cm(-2) with an overpotential that only increases 6 mV whereas the fcc sample increases 50 mV and the commercial Pt/C more than 350 mV. The significant variation in the stability of two Ru allotropes could be attributed to the difference in their crystal symmetries. Thus, this study underlines the importance of controlling the crystal structure of nanoparticle electrocatalysts and underlines the potential of using relatively cheaper Ru as an alternative to Pt for HER in alkaline conditions.