A number of structural analysis methods were employed to investigate the microstructures of ion-beam co-sputtering of CoxAg1-x (0 less than or equal to x less than or equal to 100 at %) granular films. For x = 22 at %, the sample which has the optimal giant magnetoresistance at room temperature, there exists either crystallized or highly disordered regions shown by high-resolution electron microscopy. At the boundary between cobalt granules and the silver matrix, lattice mismatch was formed, leading to roughness of the interfaces. X-ray diffraction and transmission electron microscopy revealed that the samples had fcc structure at low x, with (111) texture, and the hcp structure gradually appeared as x > 75 at %. Relative lattice expansion was observed as x increased.