In this study, a line balancing problem, which considers flexibility constraints of operations, has been presented to respond fast changing sectoral market demands in textile and apparel industry. This problem, called as the flexibility constrained line balancing problem (FCLBP) in lean manufacturing, takes into account operation flexibilities and assigns them to the available operators using the flexibility boundaries. The material of the study is the operation details that will be balanced the line in the sewing department as in (1). The method of the study is integer mathematical programming and meta-heuristic algorithm. Using the integer model, minimum idle time per operator in a given production range will be obtained and, furthermore, using the genetic algorithm, market demands will be responded in different balanced number. Lastly, using the algorithm, software has been programmed in C# to be used in the textile and apparel industry. Also, the high-efficiency balancing results will be obtained by means of the software.