Owing to their sessile lifestyle, it is crucial for plants to acquire stress tolerance. The function of heat-shock proteins, including small heat-shock proteins (smHSPs), in stress tolerance is not fully explored. To gain further knowledge about the smHSPs, the gene that encoded the cytosolic class II smHSP in Arabidopsis thaliana (At-HSP17.6A) was characterized. The At-HSP17.6A expression was induced by heat and osmotic stress, as well as during seed development. Accumulation of At-HSP17.6A proteins could be detected with heat and at a late stage of seed development, but not with osmotic stress, suggesting stress-induced post-transcriptional regulation of At-HSP17.6A expression. Overproduction of At-HSP17.6A could increase salt and drought tolerance in Arabidopsis. The chaperone activity of At-HSP17.6A was demonstrated in vitro.