The ongoing development of the concept ‘Mobility as a Service (MaaS)’ along with Shared Mobility contributes to the integration of transportation systems. Several MaaS or similar services are already in operation. The perceived quality of MaaS by the users varies significantly, and no general method is proposed to evaluate the service quality. This scantiness is identified as the research gap. The objective of the research is to elaborate a quantitative method to assess MaaS services. The research question is how to assess the quality of MaaS, and how to transform the qualitative description into quantitative numerical values, namely, the quality index and the level of quality. Since user expectations towards the importance of criteria are taken into consideration, the modified triangular fuzzy analytic hierarchy process method is introduced to calculate the weights of criteria. A quantitative method to calculate the quality index and to assign the quality level has been elaborated. Ten MaaS services are assessed with the method. It was found that the journey comfort is regarded with significant importance among the respondents. Furthermore, the quality index of MaaS services is not high; accordingly, the service quality requires continuous improvement. Our method facilitates decision-making when planning MaaS to identify the expected service attributes.