Pb isotopes are very sensitive to continental crustal contamination. With these isotopes, we are able to discriminate the contribution of the lower crust from that of the upper crust. With the objective of constraining the genesis of arc magmas by focusing here on the role of the continental crust, we propose a geochemical study on eruptive products of the Cotopaxi volcano. This choice is based on the fact that Cotopaxi is constructed on a thick continental crust and that its magmatic series span a large geochemical diversity, from basaltic andesites to rhyolites (Garrison et al., 2006, Garrison et al., 2011). We provide here 23 new high-precision Pb isotope data obtained on tephras, covering the range from andesites to rhyolites, over a period ranging from pre-Holocene to historical times. Isotopes variations are comprised between 18.980 and 18.923 for 206 Pb/ 204 Pb, 15.629 and 15.640 for 207 Pb/ 204 Pb and 38.717 and 38.765 for 208 Pb/ 204 Pb. Comparing these results with published data, we observe that our data have restricted