Phosphotungstic acid (PW) was successfully immobilized on imidazole poly(ionic liquid) (PIL) via ion-exchange for the catalytic isomerization of alpha-terpineol to 1,8-cineole. TG, XRF, FT-IR, XRD, NH3-TPD and DSA were subsequently used to characterize the PW/PIL catalyst. High catalytic activity and stable performance of the catalyst were achieved. A series of 1-alkyl-3-vinylimizolium bromide monomers (alkyl from ethyl to hexadecyl) were applied for the synthesis of PILs as the supports of PW. Results revealed that the lipophilicity of longer chain alkyl PIL exposed the PW active sites efficiently, which consequently enhanced the alpha-terpineol conversion and reduced the reaction time.