In this paper, thermal modeling of a double slope active solar still has been carried out on the basis of energy balance of east and west glass covers, water mass and basin liner under natural circulation mode. The thermal model of distillation system has been validated for hourly data for inner and outer glass cover temperatures, water temperature and the yield. The hourly thermal and exergy efficiency of active solar still have also been evaluated for 0.03 m water depth. It has been observed that the thermal efficiency of double slope active solar still is lower than the thermal efficiency of double slope passive solar still. However, the exergy efficiency of double slope active solar still is higher than the exergy efficiency of double slope passive solar still. All numerical calculations have been performed for a typical day in the month of March 2008 for the composite climate of Ghaziabad (28 degrees 40'N, 77 degrees 25'E). UP, India. (C) 2009 Elsevier B.V. All rights reserved.