The relaxation kinetics poly(3,4-ethylenedioxythiophene) (PEDOT) electrodeposited on platinum electrode surface were studied in a room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (EMITFSI), by means of large amplitude potential step experiments. The influence of the applied potential and the film thickness were analyzed. We have developed a kinetic model allowing the determination of the kinetic features. Accordingly, two time or kinetic constants, for both oxidation and reduction that were in relation to PEDOT film morphology were determined. These kinetic constants seemed independent to the applied potential. We showed that the kinetic constants for the fast process depended upon the thickness of the polymer film. However, the time constant for the slow process was virtually independent of the film thickness. We have introduced dimensionless variables that can be used to analyze the global process. Accordingly, the kinetics for the oxidation were faster than that of reduction. These results were in agreement with the ions transfer mechanisms during the redox switching of PEDOT in EMITFSI in which a departure of cation occurred during the oxidation.