We report the first investigation of ruthenium electrodeposition on Au(111) from an ionic liquid, 1-butyl-3-methylimidazolium dicyanamide, which exhibits sufficient solubility of RuCl3 at room temperature. Employing cyclic voltammetry and in situ electrochemical scanning tunneling microscopy (EC-STM) we find that Ru(IV)-complex formation is a necessary prerequisite for Ru metal deposition from this ionic liquid. The corresponding oxidation reaction occurs at an anodic potential of similar to 0.6 V vs. Pt/Pt(II). Thin Ru films of similar to 5 nm average thickness and with a relatively homogeneous morphology have been grown with a very slow growth rate of 0.1 nm min (1). The metallic nature of these films is proven by X-ray photoelectron spectroscopy. (C) 2008 Elsevier B.V. All rights reserved.