A successful implementation of a mixed-model U-line requires solutions for balancing and sequencing problems. This study proposes an approach for simultaneously solving the balancing and sequencing problems of mixed-model U-lines. The primary goal of the proposed approach is to minimize the number of workstations required on the line (Type I). To meet this aim, the proposed approach uses such a methodology that enables the minimization of the absolute deviation of workloads among workstations as well. In terms of minimizing the number of workstations required on the mixed-model U-line, as well as minimizing the absolute deviation of workloads among workstations, the proposed approach is the first method in the literature dealing with the balancing and sequencing problems of mixed-model U-lines. The newly developed neighborhood generation method employed in the simulated annealing (SA) method is another significant feature of the proposed approach. An illustrative example to clarify the solution methodology is presented. Some problem factors and algorithm parameters that may affect the performance of the approach are also tested by a comprehensive experimental study.