Calmodulin (CaM) is a ubiquitous, multifunctional calcium (Ca²⁺) sensor that exists in all eukaryotes . Calmodulin-binding proteins (CaMBPs) play important roles in various signal pathway of calmodulin. The finding of new CaMBPs will be useful for illustrating mechanism of CaM implicating in plant growth and development. Yeast two-hybrid system is an effective method for studying protein-protein interactions in vivo. In the study of plant signal transduction, many important signal transduction molecules were obtained by this system. Here, Arabidopsis flower were used as the material. The Yeast two-hybrid library of Arabidopsis flower was constructed by co-transforming yeast strain AH109 with ds cDNA, pGADT₇-rec and pGBKT₇-ACaM2. A positive clone was identified. DNA sequencing and analysis indicated that this cDNA clone encodes calmodulin-binding protein AtIQD26. The AtIQD26 protein contains a plant-specific domain of 67 conserved amino acid residues, referred to as the IQ67 domain(IQD), which is characterized by a unique and repetitive arrangement of three different CaM recruitment motifs, known as the IQ, 1-5-10, and 1-8-14 motifs. Yeast two-hybrid analysis and gel overlay experiments demonstrated that AtIQD26 interacted with CaM both in the presence or absence of Ca²⁺. A striking feature of AtIQD26 is the high isoelectric point (～10.6) and frequency of serine residues (～10%). To uncover potential roles for AtIQD26, a series of expression vectors were constructed about it, and the relative transgenic works were finished. Using these transgenic lines, the tissue expression and the subcellular localization of AtIQD26 were studied. Fusion GFP reporter showed that AtIQD26 was located at the nucleus and near cytoplasm membrane. GUS histochemical assay showed that AtIQD26 had characteristic of universal tissue expression, especially in the renascent tissue. Interaction of AtIQD26 with CaM and the presence of predicted CaM binding sites in it suggest that AtIQD26 is a new member of CaM targets. The basic isoelectric point and its potential nuclear localization suggest that AtIQD26 links Ca²⁺ signaling pathways to the regulation of gene expression. Expression similarity indicates that AtIQD26 combined with CaM to regulate plant development and growth.