Selaginella tamariscina, one of the most primitive vascular plants, can remain alive in a desiccated state and resurrect when water becomes available. To evaluate the nature of desiccation tolerance in this plant, we compared the composition of soluble sugars and saturation ratios of phospholipids (PLs) between hydrated and desiccated tissues of S. tamariscina using gas chromatography. In this study, differences in gene expression and ABA contents were also analyzed during dehydration. The results revealed that trehalose (at >130 mg g(-1) DW) was the major soluble sugar, and low saturated fatty acid content in PLs (0.31) was maintained in both hydrated and desiccated tissues. In addition, the ABA content of S. tamariscina increased 3-fold, and genes involved in ABA signaling and cellular protection were up-regulated while photosystem-related genes were down-regulated during dehydration. The biochemical and molecular findings suggest that both constitutive and inducible protective molecules contribute to desiccation tolerance of S. tamariscina.