The thermotropic liquid crystalline behavior of a new kind of amphiphilic polymer without mesogens is reported. The existence and structure for the polymeric mesophase are confirmed and characterized by DSC, X-ray diffraction, optical polarized microscopy, and temperature-dependent FTIR. Due to strong interactions between pendent long alkyl chains, we conclude that some hydrophobic semirigid rods form and are responsible for mesophase formation. Moreover, the flexible polymer network might act as a unique "spacer" group and also assist in mesophase formation.