Background <p>Emotional instability represents a significant psychological concern among university students, characterized by unpredictable emotional fluctuations and regulatory difficulties. Dark personality traits—including narcissism, psychopathy, Machiavellianism, and sadism—have emerged as potential risk factors, yet their relationship with emotional instability through impulsivity remains underexplored.</p> Method <p>This descriptive-correlational study employed structural equation modeling to examine 347 undergraduate students from Islamic Azad University, Tabriz Branch, during 2023–2024. Participants were selected through multistage cluster sampling and completed the Emotional Adjustment/Instability Scale, Dark Tetrad Personality Measure, and Barratt Impulsiveness Scale. Data analysis utilized Pearson correlation and structural equation modeling via SPSS 26 and AMOS 24.</p> Results <p>Findings revealed significant positive correlations between dark personality traits, impulsivity, and emotional instability (<i>p</i> &lt; 0.05). Direct effects showed that dark traits significantly predicted impulsivity (β = 0.537, <i>p</i> &lt; 0.001) and emotional instability (β = 0.258, <i>p</i> = 0.037), while impulsivity significantly predicted emotional instability (β = 0.474, <i>p</i> &lt; 0.001). The indirect effect of dark traits on emotional instability through impulsivity was also significant (β = 0.255, <i>p</i> = 0.003). The model explained 28.9% of the variance in impulsivity and 42.3% in emotional instability, demonstrating acceptable fit indices (e.g., RMSEA = 0.011, CFI = 0.998).</p> Conclusion <p>Results indicate that dark personality traits predispose students to heightened impulsivity, which subsequently contributes to greater emotional instability. These findings highlight the importance of targeted interventions addressing both personality-related vulnerabilities and impulse regulation in university settings.</p>