<p>Water diffusion in silicate melt is an important process modulating magmatic water content and facilitating bubble growth and volcanic eruption. The increase of water diffusivity with increasing water content was ascribed to a dominant role played by molecular H₂O (H₂O_<i>m</i>), but the contribution of hydroxyl (OH), especially at water content &lt; 2 wt%, was recently recognized for intermediate to mafic melts. The mechanisms of water diffusion in felsic melts therefore also require reexamination. In this study, we carried out two series of water diffusion experiments in low-H₂O rhyolitic melts: (1) diffusion couple experiments at 1473 K and 1 GPa in piston cylinder apparatus for melts with 0–2 wt% total water (H₂O_<i>t</i>); (2) hydration experiments at 773–1873 K and 0.1–1 GPa in cold-seal pressure vessel and piston cylinder apparatus for melts with &lt; 0.15 wt% H₂O_<i>t</i>. The diffusion profiles in the quenched products measured with FTIR microspectroscopy were fitted with both error function and speciation-based diffusion models. The diffusion couple profiles indicated an increase in water diffusivity with increasing water content. At H₂O_<i>t</i>&lt; 0.15 wt%, a change in slope at ∼1373 K was found in the Arrhenius plot of water diffusivity, and the data at 1373–1873 K were in line with fluorine diffusivity. These observations indicate that while H₂O_<i>m</i> dominates water diffusion in rhyolitic melt at H₂O_<i>t</i>&lt; 0.3 wt% or <i>T</i>&lt;1273 K, OH diffusion makes a huge contribution to water diffusivity at H₂O_<i>t</i>&lt; 0.15 wt% and <i>T</i>&gt;1373 K, despite that a vast majority of OH is attached to the silicate network. We provide an updated quantitative model for water diffusivity in rhyolitic melt with the incorporation of OH contribution. Oxygen diffusion boosted by OH can explain the discrepancy between experimental O diffusivity in “dry” rhyolitic melt (with actually a few hundred µg g⁻¹ water) and the value prescribed by the Eyring relation.</p>