Excitation of upper hybrid (UH) waves from ordinary-mode (O-mode) electromagnetic waves via large-scale electron density gradient in the upper hybrid resonance (UHR) region of the ionosphere is investigated. The model used is that of a driven harmonic oscillator in which the electron drift velocity induced by the O mode beats with the local electron density to produce a source current that drives the excited UH waves. It is found that strong excitation of UH waves occurs in the UHR region, implying enhanced damping of the incident O mode. ¿ American Geophysical Union 1996