We present in this paper some determinations of Hf and Y in zircons using X-Ray fluorescence method. Most of the results are in good agreement with those of the literature. In igneous rocks of the calco-alkaline series, the Zr/Hf ratios of zircons, wich range from 48 to 29, decrease with the color index, i.e. from diorites to granites. In the alkaline series, zircons with the lowest Hf content are found in nepheline syenites. Y shows the same trend of variation. The Zr/Hf ratios of zircons from metamorphic rocks may be considered as normal. Zircons of albitized granites are poor in Hf whereas those of autometasomatic granites are very rich in both Y and Hf. Zircons of effusive rocks have Zr/Hf ratios more variable than those of plutonic rocks of the same composition.