Conjugated Schiff’s bases (-CH=CH-CH=N-) of 4-(alkoxycinnamylidene)-4’-nitro anilines (AN) were successfully synthesized by the Wittig reaction. Most of the homologues series exhibit lower clearing temperatures than those reported for the 4-(nitrocinnamylidene)-4’-alkoxyanilines (NA). A plausible reason may be due to the higher extent of non-coplanarity in the AN system than in the NA system. Comparison of the conjugated Schiff’s bases with the simple Schiff’s bases suggests that the addition of one more double bond increases the phase transition temperatures and stabilities of the mesophases. It seems that the increase of molecular length contributes to these effects.