Abstract: The invention concerns a method for measuring the leakage rate of an activated carbon filter, characterised in that it comprises the following steps: injecting into the circuit comprising the filter to be tested a gas mixture comprising a carrier gas and a gas trappable by said filter to be tested, sampling, upstream and downstream of the filter, a relative amount of said gas mixture in storage means, measuring the amount of trappable gas contained in each of the storage means using a photoionisation chromatograph, determining the leakage rate by comparing the relative amount of trappable gas present downstream and the relative amount of trappable gas present upstream of the filter.