Objective: To examine the association between impulsivity and self-harm/suicide.Methods: We recruited students from 10 high schools by suggestive sampling.They answered computerized questionnaires including questions about self-harm/suicide, substance use, Patient Health Questionnaire 9 (PHQ9), Multi-dimensional Support Scale (MDSS) and Chinese Version of Barratt Impulsiveness Scale (BIS-11).Results: 1230 adolescents were recruited.308 from Taipei City; 922 from New Taipei City.M∶ F =496 (40.3%)∶ 734 (59.7%).Mean age 16.5 y/o (STD 0.64).23.6% had deliberate self-harm behaviours (DSH).42.6% ever had suicide idea.14.5% ever planned suicide.5.7% tried to suicide during their self-harm events.In univariate analyses, BIS-11 score were correlated with numbers of self-harm behaviours, ever had suicide idea, ever planning suicide and suicide attempts.Four logistic regression analyses were used to find whether impulsivity predicts lifetime DSH, suicide ideation, and suicide plan and suicide attempt.In these analyses, sex, number of physical illness, whether smoking or use of illicit substance, frequency of alcohol use, scores on PHQ9, MDSS, BIS-11 were entered at once as independent variables into the model.BIS-11 score predicted only DSH and ever planning suicide.Sex, PHQ9 score, drinking and smoking were also correlated with DSH, suicide idea and planning suicide.The only predictor of suicide attempts was PHQ9 score.Conclusion: Consistent with other studies, impulsivity was correlated with self-harm behaviours.Other studies found controversial results about impulsivity and suicide.We failed to prove the association with impulsivity and suicide, but found depression (PHQ9 score) predicted suicide better.