Using direct sulfation of cellulose, we prepared sulfated cellulose (CS) with various degrees of substitution of sulfate groups (DS), which we used as dopants for PEDOT. PEDOT/CS were prepared via in situ chemical oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) in an aqueous CS solution. Films of the obtained PEDOT/CS were formed using spin-coating. As a reference, a PEDOT/PSS film was also formed. The electrical conductivity of the PEDOT/CS film with a DS of 1.03 was 0.576 S m(-1). In contrast, the electrical conductivity of the PEDOT/PSS film was 0.0153 S cm(-1). Using Raman spectroscopy, we found that the 1400 and 1500 cm(-1) bands correspond to the C-alpha=C-beta vibrations in the five-member PEDOT ring. Compared with the band of the PEDOT/PSS film, the band of the PEDOT/CS film red-shifted from 1437 to 1433 cm(-1) and narrowed. We attributed the increased electrical conductivity of the PEDOT/CS film to a greater proportion of the quinoid structure than in PEDOT contained in PEDOT/PSS.