Objectives : Significant progress has been made in understanding psychosocial, psychological, and environmental factors associated with suicide. However it is only recently that attention has been paid to the understanding of the neurobiology of suicide. The aim of this study was to examine the relationship between platelet serotonin level and suicidal behavior and psychological features of the suicidal attempters. Methods : After a suicidal attempt platelet serotonin level was measured from 21 patients and compared it with those from depression patients and normal controls. Also MMPI, HAM-D, Barratt impulsiveness scale(BIS) were done to evaluate their psychological features. Results : 1) There was no significant difference in sex ratio of the suicidal attempters. 2) There was no significant difference in platelet serotonin levels among three groups. 3) The analysis of MMPI revealed that the scores of D, Hs, Pt in clinical scales were significantly higher in suicide patients and scores of D, Pa, Si were in depression patients. 4) The HAM-D score was significantly higher in depression and suicide patients, especially in depression patients. 5) The analysis of Barratt impulsiveness scale revealed that the scores of nonplanning, motor and cognitive impulsiveness scale were significantly higher in suicide patients. Conclusions : There was no significant difference in platelet serotonin levels among three groups. However the analysis of psychological features revealed significant differences. Therefore we concluded that psychological examinations are benefit to evaluate the suicidal tendency.