Introduction: Human Immunodeficiency Virus /Acquired Immunodeficiency Syndrome (HIV/AIDS) has become increasingly public health problem worldwide. Particularly in developing countries’ higher institutions like Ethiopia. The victims are youngsters; productive age of the population. The primary prevention and control of the spread of HIV/AIDS infection is through awareness and changing behavior remains at the highest priority. However few studies have been conducted among university students of Ethiopia on their self-efficacy of Human Immunodeficiency Virus/Acquired Immunodeficiency Syndrome prevention and control. Hence, this research was intended to investigate the Knowledge and self-efficacy of Madda Walabu University Undergraduate Students on HIV/AIDS.Methods: An institutional-based cross-sectional the study design was conducted among 605 under graduate students of MaddaWalabu University students were selected using random sampling and data were collected using by structured self-administered questionnaire. Descriptive independent sample t-test and ANOVA were computed to analyze the data. Result: This study result shows that among the total study participants, majority of the students (81.3%) has ever experienced sexual relationship. Nearly half (52.4%) of the students use condom during sexual intercourse consistently. About half (49.37%) of them had moderate level of knowledge regarding Human Immunodeficiency Virus/Acquired Immunodeficiency Syndrome infection, and of which only 28.4% of them had regular sexual partner. Students’ level of knowledge regarding Human Immunodeficiency Virus/Acquired Immunodeficiency Syndrome significantly predictor of their level of self-efficacy and condom use (R = 0.445 and R2 = 0.198). Conclusion: The knowledge students have on human immunodeficiency virus/acquired immune deficiency syndrome, significantly predicts self-efficacy of protecting oneself from HIV/AIDS. Most students at the age of adolescence habit sexual intercours