The aim of this study was to investigate the influence of the cell wall of the microalga Chlamydomonas reinhardtii (C. reinhardtii) on its anaerobic digestion (AD) by comparing the AD of C. reinhardtii 6145 and of its mutant without cell wall C. reinhardtii cw15, assessing simultaneously the influence of the cell wall on anaerobic co-digestion of these strains with a carbon-rich substrate, olive mill solid waste (OMSW). The OMSW is the main by-product from two-phase olive oil manufacturing process. Biochemical methane potential (BMP) tests of the sole substrates and different mixtures (OMSW-microalgae) (85%-15%, 75%-25%, 50%-50%) were carried out. The results showed that the cell wall was not hindrance and became an advantage by releasing intracellular biomass to be degraded slowly. The influence of the substrate composition in the mixtures of OMSW and Chlamydomonas reinhardtii (6145 and cw15) was assessed through the calculation of performance and kinetic parameters by using the Transference Function model. The mixture 50% OMSW-50% C. reinhardtii 6145 allowed the highest methane yield (542 +/- 4mL CH4/g VS) and also resulted in one of the highest maximum methane production rates, Rmax (129 +/- 3mL CH4/(g VS.d). (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.