Femtosecond luminescence dynamics of poly (phenylacetylene) (PPA) and poly (1-phenyl-1-butyl) (PPB) were investigated. PPA shows much larger red shift (～160 meV) of luminescence spectrum than PPB (～60 meV). Ultrafast energy-dependent luminescence decay was observed in PPA, but it is absent for PPB. We attribute the luminescence dynamics observed in PPA and PPB to the exciton migration within the inhomogeneous distribution of conjugated chains. The length of side groups plays an important role in the luminescence dynamics of substituted polyacetylenes.