The aim of this study is to investigate the assembly line balancing problems (ALBP) in the garment industry. For many years, manual methods of balancing production lines have been used, while computer-based methods can determine the number of workstations and activities of each work station with high efficiency. This research investigates the application of Flexible Line Balancing (FLB) software in balancing of work pants sewing process. For this purpose, the work pants sewing line and the sequence of activities in the production process were identified, and then the balanced sewing line was designed and suggested using FLB software. First, the results show five workstations with relatively the same workload, so that the idle time for each station is at least 10 seconds. In this way the line balancing efficiency is equal to 84.8%. On the other hand, the examination of the number and variety of machines required in each work station leads to at least 13 sewing machines for the pants sewing process. In this regard, the ability of activities separation at the FLB was investigated in order to reduce the number of machines and the results showed that it is possible to plan the workstations in such a way that three less machines are required. In this case, the line balancing efficiency shows a 2% increase compared to the previous case. In general, the production cycle time and the limitations of sequence and prerequisite activities are well considered in this software so that the workload of each station is almost the same. The results of this paper could be used in determining the number of work stations and assigning activities in the production planning for garment manufacturing.