Anionic reactions in the gas-phase clusters of olefin molecules followed by collisional electron transfer from a high-Rydberg krypton atom, Kr-**, were investigated systematically by use of mass spectrometry. The olefin molecules used in the present study are 2-chloroacrylonitrile (CAN), acrylonitrile (AN), acrylonitrile-d(1) (AN-d(1)), methacrylonitrile (MAN), and styrene (ST). The results are enumerated as follows : (1) Negative ion mass spectra for all the compounds except for styrene exhibit nonstoichiometric mass peaks assigned to [(CAN)(n) - mHCl](.-), [(AN)(n) - Y](.-) (Y = H, H-2, HCN, and H-2 + HCN), and [(MAN)(n) - HCN](.-) which are formed by liberating neutral species, such as HCl, Y, and HCN, from the corresponding intact anions. (2) Elimination of the neutral species was observed only in the cluster anions with n greater than or equal to 2. (3) Intensity enhancement at n = 3 was observed in the intensity distributions of the product anions from the clusters of CAN, AN, and MAN. (4) The elimination reaction proceeded more extensively in a cluster composed of molecules having a more electronegative substituent group. These results show that intracluster anionic polymerization is initiated by electron attachment, and the elimination reaction follows. The trimeric species are produced preferentially as a consequence of formation of a cyclic molecular anion in the cluster and subsequent evaporation of unreacted monomers. A hydrogen-bonded cyclic structure is proposed for a neutral trimer in order to explain the preferential cyclization reaction within the cluster anion.