This research explores the impact of social media influencers (SMIs) on consumer purchase intentions in China's luxury cosmetics market. China's luxury cosmetics market has grown rapidly, with urban women aged 20 - 40 being major consumers. SMIs, leveraging source credibility (attractiveness, expertise, trustworthiness, similarity), have become crucial in influencing consumer decisions. High - credibility SMIs can form parasocial relationships (PSR) with followers, which play a key role in driving purchases. However, issues like lack of transparency in commercial partnerships challenge this influence. A cross - sectional quantitative survey of 385 urban women in Beijing was conducted. Data was analyzed through descriptive statistics and partial least squares structural equation modeling. The results show that all dimensions of source credibility significantly and positively affect purchase intention. PSR also significantly mediates the relationship between source credibility and purchase intention. This study contributes to understanding influencer marketing by integrating relevant theories. For brands, it implies that partnering with credible SMIs and fostering PSRs can enhance marketing effectiveness. Nevertheless, the study's focus on a specific demographic in Beijing limits its generalizability. Future research could cover more diverse groups and markets to gain a broader perspective.