The conformational mode change of the stiff alkylated polymer, poly(3-dodecyl thiophene) (PDDT), with a flexible comb-like coil poly(octadecyl acrylate) (PODA), and the effect of intermolecular interaction between these two alkylated polymers with different chemical structure of the backbone were investigated using UV-Vis spectroscopy, Fourier transform infrared(FTIR) spectroscopy, differential scanning calorimeter(DSC), and wide-angle x-ray diffraction(WAXD). In addition to the characteristics of thermochromism, a homogeneous one phase was observed above 175 degrees C when the PODA content was 10 wt % or less. Increased conductivity in the PDDT/PODA blend due to the highly conjugated pi-system of PDDT backbone was observed in the presence of nonelectroactive PODA. A red-shift of absorption maximum of PDDT/PODA blend observed in solid state at room temperature, From the FTIR spectra, the gauche-trans conformational structure change of methylene units was investigated in two alkylated polymer blends. The increase of combined heat of fusion of the alkyl side chain melting of PDDT and the endothermic peak of PODA, as well as the interlayer d-spacing of PDDT main chain were also observed with the addition of PODA in blends. A more ordered conformational structure of rigid rod backbone of PDDT was induced due to the attractive intermolecular interaction which can cause cocrystallization between the alkylated side chains of two polymers.