Iron, Cu and Zn stable isotope systems are applied in constraining a variety of geochemical and environmental processes. Secondary reference materials have been developed by the Institute of Geology, Chinese Academy of Geological Sciences (CAGS), in collaboration with other participating laboratories, comprising three solutions (CAGS-Fe, CAGS-Cu and CAGS-Zn) and one basalt (CAGS-Basalt). These materials exhibit sufficient homogeneity and stability for application in Fe, Cu and Zn isotopic ratio determinations. Reference values were determined by inter-laboratory analytical comparisons involving up to eight participating laboratories employing MC-ICP-MS techniques, based on the unweighted means of submitted results. Isotopic compositions are reported in per mil notation, based on reference materials IRMM-014 for Fe, NIST SRM 976 for Cu and IRMM-3702 for Zn. Respective reference values of CAGS-Fe, CAGS-Cu and CAGS-Zn solutions are as follows: δ56Fe = 0.83 ± 0.07 and δ57Fe = 1.20 ± 0.13, δ65Cu = 0.57 ± 0.06, and δ66Zn = −0.79 ± 0.12 and δ68Zn = −1.65 ± 0.24, respectively. Those of CAGS-Basalt are δ56Fe = 0.15 ± 0.07, δ57Fe = 0.22 ± 0.10, δ65Cu = 0.12 ± 0.08, δ66Zn = 0.17 ± 0.13, and δ68Zn = 0.34 ± 0.26 (2s). © 2018 The Authors. Geostandards and Geoanalytical Research © 2018 International Association of Geoanalysts