An artificial material coated with a laminin-apatite composite layer on its surface would be useful as a percutaneous device with cell-adhesion properties and good biocompatibility. The present authors recently prepared such a composite by a liquid-phase coating process in which a surface-modified material was immersed in a laminin-containing calcium phosphate solution (LCP solution) supersaturated with respect to apatite. As a result of this coating process, however, the material increased in surface roughness, which may have an adverse effect on the prevention of bacterial infection. In the present study, a reduction of the surface roughness of the laminin-apatite composite layer was attempted by adding MgSO(4) to the LCP solution as an inhibitor of apatite crystal growth. The surface roughness, Ra, of the resulting laminin-apatite composite layer decreased from approximately 0.43 to 0.31mum upon increasing the MgSO(4) concentration in the LCP solution from 0 to 1.5mM, while retaining its cell adhesion characteristics. The thus-obtained material, having a laminin-apatite composite coating with reduced surface roughness, has potential as a material for percutaneous devices with improved resistance to bacterial infection through the interface between the device and the skin.