A near-infrared imaging study of the evolved stellar populations in the dwarf spheroidal galaxy Leo I is presented. Based on JHK observations obtained with the WFCAM wide-field array at the United Kingdom Infrared Telescope, we build a near-infrared photometric catalogue of red giant branch (RGB) and asymptotic giant branch (AGB) stars in Leo I over a 13.5arcmin^2^ area. The V-K colours of RGB stars, obtained by combining the new data with existing optical observations, allow us to derive a distribution of global metallicity [M/H] with average [M/H]=-1.51 (uncorrected) or [M/H]=-1.24+/-.05(int)+/-0.15(syst) after correction for the mean age of Leo I stars.