Smectic A (S-A) liquid crystalline phase developed from a new kind of mesogen-jacketed liquid crystalline polymer (MJLCP) whose mesogenic side groups are asymmetrically bonded to the main-chain was first reported. Two series of MJLCPs, poly[4,4'-bis(4-butoxyphenyloxycarbonyl)-2-vinylbiphenyl] (PBP2VBP) and poly[4,4'-bis(4-butoxyphenyloxycarbonyl)-3-vinylbiphenyl] (PBP3VBP) with different molecular weights were designed and synthesized via atom transfer radical polymerization successfully. The chemical structures of the monomers were confirmed by elemental analysis, mass spectrometry and H-1 NMR. The molecular characterization of the polymers was performed with H-1 NMR, gel permeation chromatography, and thermogravimetric analysis. Their phase structures and transitions were investigated by differential scanning calorimetry, wide-angle X-ray diffraction and polarized light microscopy experiments. The experimental results suggest that the polymer (PBP2VBP and PBP3VBP) with asymmetry mesogenic core can develop into a well-defined smectic A (S-A) phase. This implies that the polymer molecules in the LC phase can be more ribbonlike rather than rodlike.