The freshwater green algae Closterium ehrenbergii has been considered as a model for eco-toxicological assessment in aquatic systems. Heat shock proteins (HSPs) are a class of highly conserved proteins produced in all living organisms, which participate in environmental stress responses. In the present study, we determined the cDNA sequences of small heat shock protein 10 (sHSP10) and sHSP17.1 from C. ehrenbergii, and examined the physiological changes and transcriptional responses of the genes after exposure to thermal shock and toxicants treatments. The open reading frame (ORF) of CeHSP10 was 300 bp long, encoding 99 amino acid (aa) residues (10.53 kDa) with a GroES chaperonin conserved site of 22 aa. The CeHSP17.1 had a 468 bp ORF, encoding 155 aa with a conserved C-terminal α-crystallin domain. For heat stress, cells presented pigment loss and possible chloroplast damage, with an up-regulation in the expression of both sHSP10 and sHSP17.1 genes. As for the heavy metal stressors, an increase in the production of reactive oxygen species was registered in a dose dependent manner, with a significant up-regulation of both sHSP10 and sHSP17.1 genes. These results suggest that sHSP genes in C. ehrenbergii may play a role in responses to stress environments, and they could be used as an early detection parameter as biomarker genes in molecular toxicity assessments.