Cu-doped ZnFe2O4 nanoparticles (Cu-ZFNPs) with spinel structure were synthesized by a facile hydrothermal route without using any surfactant. The structure and morphology of pure ZFNPs and Cu-ZFNPs with different Cu concentrations were characterized by XRD, SEM, TEM, XPS, and FTIR measurements. Microstructural characterizations showed that the diameters of both pure ZFNPs and Cu-ZFNPs with spinel structure were approximately 50 nm, which was not significantly affected by Cu doping. Gas sensing measurements showed that Cu-ZFNPs with proper Cu concentrations were favorable for enhancing H2S sensing performance especially at low operating temperatures compared to pure ZFNPs. Gas sensors based on pure ZFNPs and Cu-ZFNPs showed reversible response and excellent selectivity to H2S at the operating temperature of room temperature to 175 degrees C. The maximum response of 37.9 was obtained for the Cu-ZFNPs to 5 ppm H2S at room temperature. The sensing mechanism was discussed in accordance with the electron depletion theory and catalytic effect of Cu doping. It indicates that the prepared Cu-ZFNPs have potential application in H2S detection at low operating temperatures.