This research proposed optimization models for fuzzy scheduling and sequencing multi-phase sample tests over multiple periods for preparation and testing stages in testing in third-party laboratories. In the preparation phase, sample tests were assigned to multi-skilled technicians at workshops. In the three-stage testing phase, tests were assigned to multi-skilled inspectors at laboratories. The scheduling model aimed at minimizing the total delay time, idle time, and overtime in all workshops and laboratories, maximizing the number of scheduled tests. Moreover, the model aims to maximize both the satisfaction on the sample completion dates, which were expressed by a fuzzy membership function, and maximizing the partial completion of samples. The sequencing model aimed to minimize the total overtime in workshops and laboratories and minimize the sum of test finish times. A real firm that offers testing …