New photo-crosslinkable side-chain liquid-crystalline methacrylate polymers comprising m-[4'-(n-cinnamoyloxyalkoxy)biphenyl-4-yloxy]alkyl groups (m, n = 2, 6) were synthesized. All polymers exhibit a nematic liquid-crystalline phase depending on the spacer length (5a-5d). Aligned thin films could be obtained using a rubbed polyimide-coated substrate, and they could be photo-crosslinked without change in the aligned structure. The photo-crosslinked film of 5d (m = n = 6) showed a stable alignment up to 300 degrees C.