Two methods have been employed to form different types of monolayers from the mixture of copper(II) and nickel(II) complexes at air-water interface. When the complexes are mixed up before they are put onto the water surface, the pi-A isotherm measurement revealed that a uniformly mixed monolayer was formed. On the other hand, when the complexes are dissolved individually and put onto the water surface successively, a mosaic monolayer of the component complexes with independent domains was formed. The domains of the copper(II) complex in the mosaic monolayer could be selectively compressed.