The South Pole of Mars is characterized by an asymmetric residual ice cap composed of water ice and CO 2 ice. On the opposite side of the residual cap, there exists an area called cryptic region which is relatively free of ice during summer time. Many fan-shaped km-scale structures apparently caused by a wind-blown system of dust-laden gas jets occurred dozens degrees of Ls before the complete sublimation of the CO 2 frost layer. We have examined the seasonal cycles of condensation and sublimation in the cryptic and non-cryptic regions by using the topographic data from the MOLA/MGS measurements. Using the MOLA topography data collected over one Martian year (1999-2001), we have studied the temporal elevation change and the seasonal cycle of the carbon dioxide frost on the southern polar caps. We have produced mapping of the seasonal CO 2 frost thickness variation for seven Ls (30°, 60°, 90°, 120°, 150°, 180°, 210°, 240°, 270° and 330°). It is found that the time variations of the CO 2 frost thickness in these two regions are quite similar. The greatest thickness of the CO 2 frost layer is about 0.76-0.78 m in both places occurs at Ls = 150°.