The intrapolymer dimer radical cation formed in poly(1-vinylpyrene) and in a novel polymer of poly(2-vinylpyrene) was studied by nanosecond pulse radiolysis measurements. Both polymers gave the main transient absorption band at 510 nm in a 1,2-dichloroethane solution at room temperature. The band was ascribed to the full-overlap dimer radical cation of the pyrene chromophore from the transient absorption spectra of three pyrene dimer model compounds; 1,3-di(1-pyrenyl)propane and 1,3-di(2-pyrenyl)propane gave the full-overlap dimer radical cation band at 510 nm, whereas 1-(1-pyrenyl)-3-(2-pyrenyl)propane gave the partial-overlap dimer radical cation band at 500 and 600 nm. On the other hand, 1-ethylpyrene and 2-ethylpyrene formed a distorted intermolecular dimer radical cation with absorption bands at <400, 510, and 510 nm.