Thin him solar cells based on ternary CuInS2 (CIS) as absorber material have reached efficiencies above 12%. A further increase of the efficiency may be achieved by improving the crystal quality of the CIS absorber layer. Subject of this work was the investigation of the effect of Ag used as Bur agent on the structural and electronic properties of CIS. For this purpose the preparation conditions and the Ag/(Ag + Cu) concentration up to 9% were varied. Scanning electron micrographs of CIS:Ag show no changes of the morphology, i.e. grain size, and the density of voids as compared to pure CIS. X-ray analysis indicates inhomogeneous solid solution formation as the CLS reflexes shift towards low 2 theta values and broaden in addition to inhomogeneous Ag distribution along the sample depth. Furthermore no systematic morphological differences between CIS and CIS:Ag as a function of the silver content can be observed. For the investigated CIS:Ag samples no band gap shift is detected. Continuous reduction of the conductivity of the absorber layers by several orders of magnitude is observed with an increasing silver content. With a higher silver content all important solar cell parameters like open circuit voltage V-oc, short circuit current I-sc and fill factor deteriorate.