The calmodulin-binding transcription activators (CAMTAs) mediate transcriptional regulation of development, growth, and responses to various environmental stresses in plants. To characterize the biological processes of soybean CAMTA (GmCAMTA) family members in response to abiotic stress, we identified 15 GmCAMTA genes from soybean (Glycine max L.) and investigated their roles in the abiotic stress response. The transcriptions of GmCAMTAs exhibited distinct circadian regulation patterns and were expressed differently in response to salt, drought, and cold stresses, except ABA. Interestingly, the expression levels of GmCAMTA2, GmCAMTA8, and GmCAMTA12 were higher in stem tissue than in other soybean tissues. To determine the roles of GmCAMTAs in the regulation of developmental processes and stress responses, we isolated GmCAMTA2 and GmCAMTA8 cDNAs from soybean and generated Arabidopsis overexpressing transgenic plants. The GmCAMTA2-OX and GmCAMTA8-OX plants showed hypersensitivity to drought stress. The water in the leaves of GmCAMTA2-OX and GmCAMTA8-OX plants was lost faster than that in WT plants under drought stress conditions. In addition, stress-responsive genes in the GmCAMTA2-OX and GmCAMTA8-OX plants were down-regulated under drought stress conditions. Our results suggest that GmCAMTA2 and GmCAMTA8 genes are regulated by circadian rhythms and function as negative regulators in development and drought stress responses.