In this article, we introduce a protocol analysis-based approach to analyze the cognitive characteristics of conceptual ecodesigning of product-service systems (PSSs). We initially present a novel and generic model to represent the lifecycle stages of solutions offered by industry and we contextualize it to PSS based offerings. Based on this representation of the PSS lifecycle stages and that of its architecture, we propose a multi-level coding scheme and a protocol analysis-based approach to analyze the distribution of designers' cognitive effort on the following three dimensions: i) different lifecycle stages, ii) different aspects of PSS architecture and iii) ecodesign activities and environmental issues. We applied this approach to analyze a conceptual PSS ecodesign case, performed in a laboratory setting by a pair of experienced practitioners. The results clearly indicate the evidence of quantitative differences in the distribution of the designers' cognitive effort on the different dimensions of PSS ecodesigning and thus, confirms the applicability and utility of the proposed approach.