Summary: Assembly line balancing by workload smoothing is very common; it aims to appropriately assign tasks to the stations of an assembly line, to ensure as similar as possible workloads for the stations. A shortcoming of the mathematical models developed in the literature is the optimization of workload smoothing when only all potential stations are considered. Therefore, the obtained solution may not be the global optimal solution and also may not be effective for real world cases. To overcome this shortcoming, some new workload smoothing criteria and their related mixed integer linear mathematical models are developed for three different settings: (1) workload smoothing optimization, when all potential stations are considered, (2) workload smoothing and minimization of the number of stations are optimized simultaneously, (3) global workload smoothing optimization regardless of the number of considered stations. The proposed formulations are associated with fewer variables and constraints compared with models previously presented in the literature and lead to better results according to an extensive numerical study. The proposed models can be applied in practice for designing the assembly lines of, inter alia, automobile and electronic equipment production systems.