Amidst globalization, the fast-food industry, notably brands like McDonald's, has attracted significant interest. McDonald's dominates in the U.S. and has seen remarkable success in markets like China. Yet, despite its global image, differences in marketing and consumer behavior exist between these nations. This study aims to dissect the distinctions between McDonald's in China and the U.S., focusing on product adaptability, advertising, and consumer behavior. The intent is to grasp how global brands localize in varied cultural environments. Historically, McDonald's transitioned from a U.S. local brand to a global powerhouse. The U.S. formed its foundational market, while China presents both vast opportunities and challenges. Key questions addressed include McDonald's product adjustments for diverse cultures and whether advertising should be country-specific. To answer these queries, this paper mixes qualitative and quantitative research. Data will be sourced from consumer surveys and interviews, and a thorough analysis of McDonald's advertising in both nations. Secondary data will also be examined for a holistic view. This approach aims to pinpoint McDonald's strategic adaptations and potentially guide other global brands in localization endeavors.