Abstract We exploit the recent James Webb Space Telescope (JWST) determination of galaxy UV luminosity functions over the redshift range z = 9–14.5 to derive constraints on warm dark matter (WDM) models. The delayed structure formations in WDM universes make high-redshift observations a powerful probe to set limits on the particle mass m _x of WDM candidates. By integrating these observations with blank-field surveys conducted by the Hubble Space Telescope (HST) at redshifts z = 4–8, we impose constraints on both astrophysical parameters (β, γ, ϵ _N, and M _c for a double-power-law star formation efficiency, and σ M UV for a Gaussian magnitude–halo mass relation) and the WDM parameter (dark matter particle mass m _x) simultaneously. We find a new limit of m _x ≥ 3.2 keV for the mass of thermal relic WDM particles at a 95% confidence level. This bound is tighter than the most stringent result derived using HST data before. Future JWST observations could further reduce the observation uncertainties and improve this constraint.