Phase behavior of a supramolecular system based on poly(4-vinylpyridine) (P4VP) and 3,4,5-tris(dodecyloxy)benzoic acid (TDBA) [P4VP(TDBA)(x), where x is the molar ratio of TDBA to P4VP repeating unit] was investigated by means of FTIR, differential scanning calorimetry, polarized optical microscopy, and X-ray scattering method. The intermolecular hydrogen bonding interaction between P4VP and TDBA is confirmed by FTIR:While almost all of the added TDBA molecules are hydrogen bonded to the P4VP chains at x < similar to 0 60, the hydrogen bonding interaction becomes incomplete at x > 0.60 and saturates at x > 0.90. The phase structure of P4VP(TDBA)(x) is composition dependent. At x < similar to 0.30, the complex is homogeneous. With similar to 0.30 < x < similar to 0.60, P4VP(TDBA)(x) forms a lamella phase, of which the long period is proportional to 1/x. Further adding TDBA causes a lamella-to-cylinder transition; At x > similar to 0.60, the lattice, parameter of the cylinder or hexagonal columnar (Phi(H)) phase decreases with increasing x. Considering the microphase separation between the polar part and the nonpolar part of alkyl tails, the lamella-to-cylinder transition can be understood using volumetric argument We consider that the large nonpolar part of TDBA enhances the microphase separation of P4VP(TDBA)(x), and moreover, the fan like shape of TDBA facilitates the formation of Phi(H) phase. We also roughly estimated the domain size of the P4VP Chains in the microphase-separated mesophase. For both the lamellar and Phi(H) phase, increasing x results in stronger confinement on the P4VP chains. During the lamella-to-cylinder transition the confinement imposed by the TDBA molecules may be partially released, which favors the Phi(H) phase formation.