A novel alternant amphiphilic polymer poly[1,4-bis(phenylethynyl)-2,5-bis(hexyloxy)benzene-alt-tetra(ethylene oxide)] was prepared. Atom force microscope (AFM) images showed that the molecular self-assembly morphologies changed from molecular nanowires to twist fibrillar architectures with the increase of the solution concentrations. Short and thin wires formed in dilute solution, while large bundles developed in relatively concentrated ones, shown by fluorescence microscope images. The photoluminescence (PL) spectra of the corresponding films indicate a self-assembly process of the polymers under slow solvents evaporation. Coplanar aggregation was confirmed through PL and photoluminescence excitation (PLE) spectra. Furthermore, the self-assembly process in polymer bulk was studied by wide-angle X-ray diffraction. To the best of our knowledge, it is the first time to reveal the change of the molecular morphologies with the altering concentration for the alternant amphiphilic conjugated polymers.