SUMMARYA full-wave analysis of the composite-metal microstrip lines is presented. The effects of the composite metal to the loss of the microstrip lines are accurately investigated, which are often avoided by other methods. The metal layers of the microstrip lines are considered as lossy inhomogeneous layers. The effects of the thickness of the Au layer and Ti layer are given, respectively. And the reasons that lead to the differences between them are discussed for the first time by analyzing the longitudinal electric field on the strip. The results are compared with other published data.