This paper provides an integrated approach for evaluating and selecting third party logistics (3PLs) service providers. It contains two phases: the first phase employs a fuzzy analytical hierarchy process to specify the weights of the evaluation criteria, while the second phase uses the technique for order preference by similarity to ideal solution to evaluate the alternatives, sequence them, and select the best option. Finally, the proposed approach was implemented for a case study with four criteria and three alternatives. After that, sensitivity analysis was developed to get deeper insights. The results manifest the impact of using different methods to find the fuzzy sets on the value of criteria. The most important factors in 3PL selection were found to be compatibility (47.17%), financial performance (25.49%), reputation (16.52%) and long-term relationship (10.82%). The paper compares between using the extent analysis method and the geometric mean technique to find the fuzzy numbers.