The photoelectrocatalytic activity of polyterthiophene (PTTh) was investigated. PTTh prepared by the vapour phase polymerisation technique was used as a working electrode. When the electrode was used in electrochemical water oxidation, illumination produced a significant increase in oxidation current at potentials beginning at ~ 100 mV below the expected water oxidation potential. Dissolved oxygen content was measured, confirming that the photostimulated process was water oxidation to oxygen. The PTTh electrode also showed photoconductivity under illumination, but its contribution was negligible in the photoelectrocatalytic experiment. These observations open the way to further development of conjugated polymer electrodes as electrocatalysts for water oxidation.