This work describes the synthesis, thermomechanical properties, and functionalization of unsaturated polyesters based on biobased cis-2-butene-1, 4-diol (cB). Under an optimized experimental process, polyesters were synthesized by melt polycondensation employing cB and α, ω-diacids with even chain length. The high molecular weight of M_w up to79.5 kDa was achieved for the poly(cis-butene dicarboxylate)s (PcBX), and meanwhile without isomerization or branching side reactions occurring in the polycondensation. Hence, cB was a suitable unsaturated diol for direct usage in the preparation of linear unsaturated polyester with high molecular mass. The result of mechanical properties indicated that cB outperforms 1, 4-butanediol in regard to enhancing the mechanical property of polyesters. Satisfactory thermal and crystal performances, broad processing window, as well as excellent mechanical properties were presented for PcBX, indicating that these synthetic biobased polyesters were promising candidates for replacing petroleum-based polyesters in practical application. Furthermore, an attempt was made to incorporate the functional group of hydroxyls in the backbones through “click reaction”, and the existence of free hydroxyls on the surface of PcBX results in their greatly improved hydrophilicity. The inserted hydroxyls greatly accelerated the degradation rate of polyesters. Overall, this paper not only offers a straightforward method for the preparation of high molecular mass unsaturated polyesters with adjustable performances, but also presents the potential of functionalization for a broad range of applications.