Objective <p>This study aims to investigate whether and how trait impulsivity differentiates suicidal ideation (SI) from suicide attempts (SA) in adolescents with Major Depressive Disorder (MDD), and the mechanisms through which impulsivity increases suicide attempt risk.</p> Methods <p>A total of 185 adolescents diagnosed with MDD and suicidal ideation were categorized into SI (<i>n</i> = 118) and SA (<i>n</i> = 67) groups based on lifetime suicide attempt history. Study variables included impulsivity, depression severity, suicidal ideation intensity, and demographic and clinical characteristics. Group difference analysis compared variables between the two groups. Multiple logistic regression and moderated mediation models were applied to analyze the relationships between impulsivity and suicidal behavior.</p> Results <p>The SA group exhibited younger age, higher depression severity, higher impulsivity, and higher suicidal ideation intensity compared to the SI group. Unadjusted logistic regression revealed that higher impulsivity was associated with higher odds of suicide attempt risk (OR = 1.03, <i>p</i> = 0.030); however, this association became nonsignificant after adjusting for covariates. Mediation analysis revealed a pattern consistent with an indirect association: trait impulsivity was statistically associated with higher suicide attempt risk via depression severity and suicidal ideation intensity, whereas its direct association was not significant. Age moderated the relationship between impulsivity and suicidal ideation intensity (B = -0.05, <i>p</i> = 0.039), showing stronger associations in younger adolescents.</p> Conclusion <p>Trait impulsivity alone does not directly differentiate suicidal ideation from suicide attempts. It is indirectly linked to suicidal behavior through the severity of depression and the intensity of suicidal ideation. The correlation between impulsivity and suicidal ideation intensity diminishes as age increases.</p>