The following photophysical properties related to the lowest triplet of poly(2-vinylnaphthalene) (P2VN) have been investigated by laser flash photolysis and pulse radiolysis: Tn← T1absorption spectrum, lifetime, extinction coefficient ϵT, quantum yield of formation φTMand triplet energy transfer rate constant kQin reaction between the biphenyl lowest triplet and P2VN. It has been found from studies of four polymers with varying degrees of polymerization (P= 109, 318, 688, and 2690) that φTMand kQbecome smaller the higher the degree of polymerization.