We report electrochemical studies and the observation of excimer emission from the conjugated polymer poly(9,9-dioctylfluorene) (PDOF) in benzene-MeCN solutions during electrogenerated chemiluminescence (ECL). The ECL emission spectrum resulting from the annihilation reaction between PDOF radical ions is characterized by two bands, one at 438 nm and a broad band centered at 610 nm, The ECL emission at shorter wavelengths is assigned to intrapolymer emission of PDOF, while the emission at longer wavelengths arises from the excited-state complex of the polymer formed in the radical annihilation reaction. The relative excimer emission from PDOF (the ratio of excimer ECL emission to intrapolymer emission) depends on polymer concentration.