In this paper, a method for measuring waveguide propagation losses by means of a Mach-Zehnder Interferometer (MZI) structure is reported. The method, based on the analysis of the transmission spectra of asymmetric MZIs, enables the propagation losses of the optical waveguides to be calculated without the requirement of identical coupling conditions for each measurement. In addition, the power imbalance of the branching structure in the MZI can also be obtained. Our theoretical analysis is supported by experimental measurements. © 2011 Elsevier B.V. All rights reserved. The authors gratefully acknowledge financial support from TEC2008-06360DEMOTEC, TEC2008-06333SINADEC and PROMETEO-2010-087R&D Excellency Program (NANOMET). The authors thank the fabrication team, A. Griol, J. Hurtado, L Bellieres, J. A. Ayucar, and F. Lopez for their countless hours of dedicated work. Gutiérrez Campo, AM.; Brimont, ACJ.; Aamer, M.; Sanchis Kilders, P. (2012). Method for measuring waveguide propagation losses by means of a Mach-Zehnder Interferometer structure. Optics Communications. 285(6):1144-1147. https://doi.org/10.1016/j.optcom.2011.11.064