Background The Ask Suicide-Screening Questions (ASQ) tool is a simple suicide screening tool developed to screen patient suicide risk (SR). The purpose of this study was to verify the reliability and validity of the ASQ tool in hospitalized patients. Methods The internal consistency and test-retest reliability of the South Korean version of the ASQ tool were verified in 99 hospitalized patients admitted to a tertiary medical institution in Seoul. To verify the correlations and validity of each convergence with other scales, the Mini-International Neuropsychiatric Interview (MINI), Patient Health Questionnaire-9 (PHQ-9), Generalized Anxiety Disorder-7 (GAD-7), and Satisfaction with Life Scale (SWLS) were also conducted to determine convergent and discriminant validity. Then, the receiver operating characteristic (ROC) curve diagnosis values for suicide and depression levels with the highest correlations were analyzed. Results As a result, Cronbach’s alpha was 0.826, and when each item was removed sequentially, Cronbach’s alpha ranged from 0.736–0.840, showing stable internal consistency. Most of the corrected item-total correlation were over 0.500; however, a relatively low correlation was shown for the fourth and fifth questions, which had values of 0.429 and 0.410, respectively. The test-retest reliability was 0.830, and the MINI and PHQ-9 showed high values of 0.872 and 0.672, respectively. The area under the curve (AUC) according to the ASQ diagnosis value was also the highest for the MINI (0.936). Conclusion The validity and reliability of the South Korean version of the ASQ tool were demonstrated. Through this validation, the ASQ tool can be used for simple suicide risk screening (SRS) in hospitalized patients.