[en] Chromospheric and transition-region activity of the intrinsically X-ray brightest contact binary XY Leo were studied using the low resolution IUE spectra: one long exposure SWP spectrum and four LWR spectra, the latter obtained at both minima and at one of the orbital quadratures. Both components seem to be similarly covered by active regions as judged from the constancy of the relative flux f(Mg2)/f(bol) = (17.6±0.6)x10^-5 (orbital average). The mean line fluxes of a few chromospheric and transition-region lines visible in the SWP spectrum were found at levels similar to those in other contact binaries of very short orbital periods. 17 refs., 2 figs., 3 tabs. (author)