Electrochemical polymerization in a room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6), has been used to prepare electrochromic poly(3-methylthiophene) (PMeT) and its more attractive derivatives: poly(3-hexylthiophene) (PHexT) and poly(3-octylthiophene) (POcT). Spectroelectrochemistry and electrochromic properties of the resulting polymers were characterized using various experiment techniques in [BMIM]PF6/CH3CN (1:1, v/v) solution. The thin films were bright red, orange red and orange yellow at its fully reduced state for PMeT, PHexT and POcT, respectively. After oxidization of these undoped polymers, the films underwent reversible change to the bright blue, blue or black blue form. These poly(3-alkylthiophene)s (PMeT, PHexT and POcT) films exhibit high chromatic contrast (46, 45 or 39%), comparative switching times (1.1, 1.4 or 1.9s), great electrochromic efficiency (250, 220 and 230cm2 C−1) and long-term switching stability. High quality electrochromic polymers were provided for the use of commercially available thiophene monomers, avoiding the use of other custom synthesized monomers.