Three blue light-emitting cyclopenta[def]phenanthrene-based conjugated polymers were synthesized using the Yamamoto coupling reaction and their optical, thermal, and electrochemical properties were examined. The results indicated that the number-average molecular weights of compounds 11, 12, and 13 were 16,400, 11,000, and 10,400, respectively. The polymers were soluble in common solvents, such as toluene, chloroform, etc. Their structures were confirmed using $^1H$ NMR, mass, and FTIR spectroscopy. Homopolymer 11 showed stable blue emission with a photoluminescence peak at 408 nm in solution and at 456 nm in thin film form. Moreover, polymers 11,12, and 13 exhibited high thermal stability up to $340^{circ}C$, $333^{circ}C$, and $380^{circ}C$, respectively.