this study deals with line balancing of BOB T-shirt model with the help of control limit analysis of the assembly lines. In this study control limes analysis is used to measure the performance of the assembly line and used to identify the bottleneck operations of the assembly line. BOB T-shirt model has 16 main operations and each operation’s time is analyzed as SMV. The main bottleneck operations are analyzed using the control limit analysis based on the SMV of each operation and those operations which are out of lower control limit and upper control limit are bottlenecks of the sewing lines of the garment section. Machine productivity and labor productivity is increased from 97.47 to 107pieces per machine from 84.2 to 92 pieces per operator respectively. And the profit of the line is increased from 40744 Ethiopian birr to 42416 Ethiopian birr per day.