This paper is concerned with the analysis of plastic deformation of bimetal co-extrusion process. Extrusion is related to large deformation of material and leads to non-homogeneous deformation within work-piece material. The mechanism of plastic deformation during the composite rod extrusion is much more complicated than that in single metal extrusion. Deformation patterns of co-extrusion of two different materials are characterized by several process parameters. In this paper, the analysis is focused to investigate the effect of contact conditions along the interface between two different materials. The rigid-plastic finite element method was applied to the analysis of co-extrusion process. The selected materials are AA 1100 aluminum alloy as hard material and CDA 110 as soft one. This type of material selection was to examine the effect of hard core and soft sleeve and vice versa in terms of deformation pattern. The initial composite billets were prepared by inserting the core material in tight (0.023mm) and weak (0.012mm) interference bonding, respectively. Four different cases of co-extrusion process in terms of material combination and interference bonding were simulated to investigate the effect of material arrangement between core and sleeve, and of bonding on the plastic zones. It is concluded from the simulation results that the plastic zones in this co-extrusion process are not influenced much by the selection of material arrangements or bonding condition between construction materials. However, it was seen from the simulation results that the extrusion ratio of each construction material, i.e. homogeneity of co-extrusion, depends much on the material arrangement and the bonding condition.