Poly(fumarate)s carrying tolane-based mesogenic side chains were for the first time prepared by radical polymerization. The phase behaviors characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD) analysis indicated that the liquid crystalline temperature ranges clearly decreased upon polymerization. This very rare behavior could be derived from the delicate balance between the mesogen structure and the rigid polyfumarate backbone.