It cannot be denied that Lean Manufacturing (LM) is a useful technique which helps to enhance the product quality and quantity, eliminate waste from the organization and reduce the production cost. Therefore, more and more companies in Viet Nam have applied LM to increase their competitiveness and meet better the demand of customer. Garment industry is a key economic sector contributing to the industrial growth in Viet Nam, especially shirt items are one of the most popular exporting products. In this study, we will present Value Stream Mapping (VSM) which is one of LM tools. This study attempts to develop VSM in a long sleeve shirt production line at Tay Do Garment Joint-Stock Company. The goal of VSM is to identify and show Value Added (VA) and Non Value Added (NVA) in the process, then, waste in terms of non-value added processes will be eliminated. Current State Map (CSM) is drawn to give details about the current state and analyze the problems which are happening in the process. Future State Map (FSM) is drawn to show the proposed changes as well as proposed benefits. As a result, there are significant improvements for lead time, VA, Work In Process (WIP) and Process Cycle Effectiveness (PCE). In addition, the simulation model will be developed based on VSM by using ARENA software. Moreover, the results are discussed elaborately.