Toray Saehan Inc.(TSI), a joint venture company, was formed between domestic synthetic fiber manufacturer Saehan and Japan’s Toray Industries Inc. in October 1999. Since then, it has achieved steady growth across total sales and profits. Then, TSI became a wholly owned subsidiary of Toray in January 2008. At present, TSI is creating the vision of a new global leader in chemical materials industry through expanding new business areas such as IT materials and environment-friendly applications. This case study raises a question, what are the critical success factors of TSI’s performance. It then highlights the successful processes of the negotiation before acquisition and post merger integration(PMI) of TSI. And it especially focuses on the strategic and cultural synergy between TSI and Toray.