In this study, optical and electrochemical properties of regioregular and soluble alkyl substituted propylenedioxyselenophene based electrochromic polymers, namely poly(3,3-dibutyl-3,4-dihydro-2H-selenopheno[3,4-b][1,4]dioxephine) (PProDOS-C4), poly(3,3-dihexyl-3,4-dihydro-2H-selenopheno[3,4-b][1,4]dioxephine) (PProDOS-C6), and poly(3,3-didecyl-3,4-dihydro-2H-selenopheno[3,4-b][1,4]dioxephine) (PProDOS-C10), which were synthesized via electrochemical polymerization, were investigated. It is noted that these unique polymers have low band gaps (1.54 &ndash / 1.64 eV) and they are exceptionally stable under ambient atmospheric conditions. For example, polymer films retained 84-96 % of their electroactivity after five thousands cycles. The percent transmittance of PProDOS-Cn (n= 4, 6, 10) films found to be between 55-59 %. Furthermore, these novel soluble PProDOS-Cn polymers showed electrochromic behavior: a color change form pure blue (L = 57.31, a = -13.18, b = - 42.68) to highly transparent state (L = 91.74, a = 2.52, b = -1.30) state in a low switching time (1.0 s) during oxidation with high coloration efficiencies (328 &ndash / 864 cm2/C) when compared to their close analogues.