Drought stress is one of abiotic stresses limiting plant growth and agricultural productivity. To further understand the mechanism of drought tolerance and identify the genes involved in this process, a genetic screen for altered drought response was conducted in Arabidopsis. One mutant with enhanced drought tolerance was isolated and named atdtm1 (Arabidopsis drought tolerance mutant 1), which has larger lateral organs, prolonged growth duration, increased relative water content and a reduced leaf stomatal density compared with the wild type. The loss of AtDTM1 increases cell division during leaf development. The phenotype is caused by the loss of a T-DNA tagged gene encoding CYCLIN-DEPENDENT KINASE C;2 (CDKC;2), which functions in the regulation of transcription by influencing the phosphorylation status of RNA polymerase II (Pol II). Here, we show that CDKC;2 affects the transcription of downstream genes, such as cell cycle genes and genes involved in stomatal development, resulting in altered plant organ size as well as drought tolerance of plant. These results reveal the crucial role of CDKC;2 in modulating both cell division and the drought response in Arabidopsis. This article is protected by copyright. All rights reserved.