Novel nickelocene based catalysts were used for polymerization of 2-butyne, 1-phenyl-1-propyne, bis(trimethylsilyl) acetylene and trimethylsilyl acetylene. The catalyst prepared in the reaction of nickelocene with organolithium compounds in the presence of alkyne was previously isolated and fully characterized. It enabled us to explain the mechanism of the polymerization. Polymerization of alkynes proceeds according to coordination-insertion mechanism. Coordinated acetylene molecule inserts into Ni-C bond. An active catalytic species of polymerization appeared to be {CpNiR} stabilized by alkyne molecule. Cyclization is catalyzed by {CpNiH} species. (C) 2004 Elsevier B.V. All rights reserved.