This research aims to identify and rank the factors influencing the quality of construction projects. The present study is based on a mixed-methods research design; a combination of qualitative and quantitative methods was used. From the perspective of purpose, it is applied research because the results of the present study are used to improve the quality of construction projects. In terms of data collection method, the present study is a descriptive survey research, and in terms of data analysis method, it was classified as quantitative research. The statistical population of the present study comprised all experts and activists in the field of construction in Tonekabon city, from which 10 individuals were selected using convenience sampling. Data analysis was performed using the Fuzzy Delphi method and Fuzzy AHP. The results of the Fuzzy Delphi analysis showed that 10 criteria including the employer's justification in terms of project quality, the employer's justification in terms of project time, the project manager's activity, the quality of project planning, the constructability of the designs, and supervision of the project's workshop activities, selecting and monitoring contractors, communication and cooperation between implementation agents, proper financial management, and selecting the best contractor are the most influential factors in improving the quality of construction projects in Tonekabon county. The ranking and importance of each criterion were determined using the Fuzzy AHP method. The results showed that the employer's justification in terms of project time, with a weight of (0.122), was in first place, the project manager's activity and the ability to build designs, with a weight of (0.108), in second place, and the quality of project planning, with a weight of (0.108), in third place. Communication and cooperation between implementation factors were ranked fourth with a weight of (0.100), sound financial management with a weight of (0.099) in fifth place, supervision of project workshop activities with a weight of (0.095) in sixth place, selection and supervision of contractors with a weight of (0.095) in seventh place, justification of the employer in terms of project quality with a weight of (0.0818) in eighth place, and selection of the best contractor with a weight of (0.809).