We report the reaction dynamics of cobalt phthalocyanine (CoPc) molecules with Bi-line structures (BLSs) on a Si(1 0 0) surface, investigated using scanning tunneling microscopy (STM). When CoPc molecules were deposited on a Si(1 0 0) surface with BLSs at room temperature, single-spot protrusions were observed in the STM image instead of four-spot images corresponding to CoPcs flat molecular structure. Moreover, domains with a c(4 x 4) periodicity appeared on the terraces of the Si(1 0 0) surface. This indicates that CoPc molecules may have decomposed on the surface by catalytic reaction with Bi atoms. (C) 2009 Elsevier B.V. All rights reserved.