We have discovered a novel Ru-based thin film metallic glass (TFMG) using combinatorial arc plasma deposition (CAPD). To search for Ru-based TFMG, alloy systems of Ru-Zr-Al, Ru-Zr-Fe and Ru-Zr-Mo were investigated by making libraries. Each library consisted of 1089 CAPD samples deposited on a substrate by CAPD. Composition of each sample is different with each other. The composition and phases of the CAPD samples were measured by energy dispersive X-ray fluorescence spectrometry and X-ray diffractometry, respectively. Results showed the amorphous regions depended on the additive elements Al, Fe or Mo. Compared with the addition of Al, the addition of Fe or Mo exhibited high amorphous forming ability. To evaluate the mechanical properties, the glass transition temperature T-g and the crystallization temperature T-x of the amorphous samples in each Ru-Zr-X alloy, larger samples having the same compositions as the typical amorphous CAPD samples were reproduced by sputtering because the CAPD samples were too small to measure the mechanical properties, T-g and T-x. Ru65Zr30Al5 and Ru67Zr25Al8 samples were found to exhibit the better fracture stress and elastic limit than conventional TFMGs, while Ru-Zr-Fe and Ru-Zr-Mo samples were found to be brittle. DSC revealed that the Ru65Zr30Al5 sample was a TFMG, with a T-g of 902 K and T-x of 973 K. (C) 2007 Elsevier B.V. All rights reserved.