In the fast-changing world of financial technology, mobile trading apps have become key tools affecting investment behavior, especially among Millennial investors. This study looks at the factors that influence stock market decisions among Indian Millennials, focusing on how they adopt and use mobile trading platforms. Using the ideas from Behavioral Finance and the Technology Acceptance Model (TAM), the research explores important factors such as perceived ease of use, trust in digital interfaces, social influence, and individual risk tolerance. The analysis examines a sample of 337 Millennial investors living in Bengaluru, India. Through factor analysis, the study identifies and assesses the main factors driving trading decisions related to mobile app usage. The results show detailed behavioral patterns and reveal the technological aspects that affect investment choices in the digital age. This research adds to the growing conversation about digital finance by providing practical insights for fintech developers, financial educators, stockbrokers, and other financial institutions. It emphasizes the need for user-friendly design, awareness of behavior, and focused financial education to better meet the changing needs of tech-savvy investors.