Companies prepare competitive strategies to win the competition in the market and industry. Recent situation is the industrial boundaries are collapsing and competitive advantage fluctuates shapely due to unlimited competition. In the situation, the ability to recognize business environmental changes, seize opportunities, and respond with agility is one of the most important core competencies for a company to create a competitive advantage. The subject of this case is a competitive strategy in the Korean hamburger market which is one of well-known consumer goods industries. In the middle of 2018, the Korean hamburger market was in a dynamic period when the external business environment had changed rapidly. First, hamburger market competition got hot as all major hamburger players as well as new premium burger players entered the growing premium burger market. Second, food delivery service market grows rapidly along with the emergence of delivery app order brokage service platform companies. Third, HMR industry grew rapidly and major convenient store chains had introduced the quality and various ready-to-eat food menu choices. It threatened food service industry to lose market size, in addition to the entire hamburger market was shrunk due to the food borne illness issues. This case study was developed as an educational purpose to present and discuss various issues in the process of preparing a competitive strategy along with a thorough analysis of internal and external business environment under the said rapidly transforming market and industry