In the copolymerizations of 1-chloro-1-octyne (ClOc) and 1-chloro-2-phenylacetylene (ClPA) with norbornene (NBE) by MoCl5-n-Bu4Sn in toluene at -20-degrees-C, both comonomers were consumed simultaneously. The GPC curves of the copolymerization products were unimodal and identical irrespective of the RI and UV (290 nm) detectors. The C-13 NMR spectra of the products exhibited the presence of cross-propagating sequences. From these results, it is concluded that the copolymerization products are copolymers and not mixtures of homopolymers. The monomer reactivity ratios were : r(ClOc) = 0.69, r(NBE) = 6.4; r(ClPA) = 1.0, r(NBE) = 3.1. The more electron-donating the ring substituent of ClPA, the more reactive the ClPA in copolymerization with NBE.