Electrothermal desorption is an electricity-promoted desorption technology developed only in the last decade. It is extremely efficient and straightforward when the adsorbent is electrically conductive, since heating can be achieved by the Joule effect. The volatile organic compound (VOC) vapors desorbing from micropores might redistribute and condense in mesopores with high concentration, which is possible since no dilution occurs. To study this problem, benzene and activated carbon were used as the working system, and a theoretical analysis was developed. In a wide temperature range up to 400℃, no VOC vapor could be condensed in mesopores with the strong micropore adsorption effect. With the weak micropore adsorption effect, however, mesopore con-densation will occur, but it only takes place in mesopores smaller than 3nm in diame-ter, and the amount is generally negligible. To prevent any possible condensation, the desorption temperature should at least equal the liquid boiling point calculated in a 2-nm capillary tube.