With the technological and economic progress, the disappearance of the boundaries has led to the continuous change in the content and volume of customer demands therefore it has revealed the necessity of the companies to respond to these changes rapidly. This necessity has also led companies to modern production systems that will meet the speed of mass production systems and the resilience capability of flexible production systems. One of these production systems is the seru production systems which started to be used in the electronics sector in Japan from the 90s. These systems divide traditional assembly lines into cells called seru, where all tasks in the production of goods are performed by one or more highly skilled employees. The aim of this study is to obtain optimal seru loading plans for seru production system that meets the speed of mass production and the product diversity capability of flexible production systems. Therefore, Seru Loading Problem, which is one of the problems encountered in seru production systems, is handled. A new mixed integer mathematical model and mat-heuristic algorithm are proposed to obtain the optimal worker and workload plan for a particular seru design. The efficiency of the results obtained from the model and the heuristic method has been shown in comparison with a real application data set obtained from the literature and it has been observed that the obtained seru loading plans are effective as a result of the comparison.