MPEJ Volume 8, No. 4, 11 pp. Received: Mar 24, 2002. Revised: Aug 13, 2002. Accepted: Aug 13, 2002. Madalina Roxana Buneci The structure of the Haar systems on locally compact groupoids ABSTRACT: We shall prove a decomposition property of a Haar system on a locally compact groupoid. Using this decomposition, we shall establish the structure of the $C^{\ast}$-algebra associated to a locally compact groupoid whose associated equivalence relation is a closed set. http://www.maia.ub.es/mpej/Vol/8/4.ps http://www.ma.utexas.edu/mpej/Vol/8/4.ps http://mpej.unige.ch/mpej/Vol/8/4.ps