AbstractThe phytohormone abscisic acid (ABA) plays crucial roles in plant development and plant responses to environmental stresses. Although ABA receptors and a minimal set of core molecular components have recently been discovered, understanding of the ABA signaling pathway is still far from complete. In this work, we characterized the function of ROP11, a member of the plant‐specific ROP small GTPases family, in the ABA signaling process. ROP11 is preferentially expressed in guard cells in all plant organs with stomata. Expression of a constitutively active ROP11 (CA‐ROP11) suppresses ABA‐mediated responses, whereas reduced expression of ROP11 or expression of its dominant‐negative form (DN‐ROP11) causes the opposite phenotypes. The affected ABA‐mediated responses by ROP11 include seed germination, seedling growth, stomatal closure, induction of ABA‐responsive genes, as well as plant response to drought stress. Furthermore, we showed that ROP11 and its closest‐related family member, ROP10, act in parallel in mediating these responses. ABA treatment does not affect ROP11 transcription and protein abundance; however, it causes the accumulation of CA‐ROP11 in the nucleus. These results demonstrated that ROP11 is a negative regulator of multiple ABA responses in Arabidopsis.