Conjugated polyanilines bearing long alkyl side chains (dodecyl PANi-12 and octadecyl PANi-18) were prepared for the purpose of obtaining well-mixed conducting polymer blends with insulating flexible polymers. The miscibility of the polyanilines and ethylene-co-vinyl acetate copolymers (EVA20 with 20 wt % of vinyl acetate and EVA70 with 70 wt %) was significantly improved by long alkyl chains of the same hydrocarbon moieties as the ethylene segments in the matrix EVA, as demonstrated by microscopic observation. PANi-18/EVA20 blends exhibit a lower critical phase separation temperature (LCST). In addition, the EVA crystallinity and the side-chain crystallinity in the miscible blends were depressed, as shown by thermal analysis and x-ray scattering. The comparison of three designed blend systems indicates that the miscibility of the polymers is determined by the hydrophobic interaction between the hydrocarbon units in the both components and by the hydrogen bonding. The solvatochromic phenomena for the blends at low miscible PANi compositions was detected by UV-visible spectroscopy. The threshold conductivities exhibit sensitivity to the morphological structure of the polymeric blends, and was lowered by improved homogenous dispersion of the conducting phase.