This study aims to investigate the impact of artificial intelligence (AI) adoption on marketing agility and competitiveness in startups operating in dynamic business environments. Employing a quantitative survey approach, data were collected from 300 startups active in information technology, e-commerce, and digital services in Iran. The data collection tool was a localized questionnaire measuring AI adoption (perceived usefulness, ease of use, and organizational infrastructure), marketing agility (responsiveness, flexibility, and speed), and competitiveness (competitive advantage and market performance). Data were analyzed using SmartPLS4 and structural equation modeling (SEM). Results indicate that AI adoption has a significant positive effect on marketing agility (β=0.71, p<0.01) and competitiveness (β=0.58, p<0.01). Additionally, marketing agility partially mediates the relationship between AI adoption and competitiveness (β=0.35, p<0.05). These findings suggest that startups effectively leveraging AI can enhance marketing agility, thereby achieving sustainable competitive advantages. It is recommended that startups invest in AI infrastructure and workforce training to maximize these benefits.