Microporous active carbons of differing structural and surface properties were studied by thermogravimetry (TGA) under controlled conditions. Weight loss curves were measured for various carbon samples wetted and saturated with water, n-butanol, benzene and n-heptane using a high-resolution thermogravimetric analyzer. This analyzer is capable of maintaining controlled conditions. Analysis of the TGA curves showed that molecules desorb from the surface via a multi-step process. For the samples wetted with liquids the initial step reflects evaporation of the excess liquid. The subsequent steps, observed for both types of samples (wetted in liquids and saturated in their vapors), reflect evaporation of adsorbate from pores and its thermodesorption from fine pores and from the carbon surface. These latter features of the TGA curves were used to obtain information about porosity and surface heterogeneity of the active carbons studied.