The objective of this study is to assess the safety and efficacy of oral YHD1023 5g or 10g on erectile dysfunction to investigate the optimal recommended dosage. Study period is 12 weeks including 4weeks of follow-up period without treatment. Study patients will fill in the international index of erectile function questionnaire and life satisfaction questionnaires.

Inclusion Criteria:

• Male volunteers of aged 20 years and older with history of organic erectile dysfunction of at least 6 months duration
• Anticipate having the same adult female sexual partner, who have no possibility of being pregnant or breast-feeding and take steps to prevent conception during the study
• The patient or legally authorized representative must sign a written informed consent, prior to the any procedure, using a form that is approved by the local Institutional Review Board after detail explanation of the purpose, contents, and characteristic of the drug
• Have Erectile Function(EF) domain score 25 and under as the result of the International Index of Erectile Function(IIEF)
• Agree to make at least 4 sexual intercourse attempts on 4 separate days with the female sexual study party during the 4-week run-in period without medication and at least 50% of attempts during this period had been unsuccessful due to insufficient erection or unable to sustain penile rigidity until ejaculation

Exclusion Criteria:

• Have history of stroke, myocardial infarction, or Coronary Artery Bypass Graft surgery within the last 6 months
• Have history of cardiac failure, unstable angina, or life-threatening arrhythmia within the last 6 months
• Shown tachyarrhythmia, heart rate over 100 times/min(e.g. arterial fibrillation, flutter)
• Presence of hypotension as evidenced by SBP/DBP < 90/50mmHg or uncontrollable hypertension as evidenced by SBP/DBP > 170/100mmHg
• Presence of diagnosed diabetes(HbA1C > 12%)
• Have history of symptomatic postural hypotension within the last 6 months
• Have history of spinal cord injury, radical prostatectomy, or pelvic surgery
• Presence of penile anatomical deformities (e.g. severe penile fibrosis or Peyronie's disease)
• Presence of hypogonadism(serum total testosterone under the reference lowest limit)
• Presence of hepatic impairment(AST or ALT > 3 times of normal upper limit) or renal impairment(serum creatinine ≥ 2.5mg/dl)
• Have history of severe gastrointestinal hemorrhage within the last 1 year
• Have history of hematodyscrasia predisposing to priapism(e.g. sickle cell disease, multiple myeloma, or leukemia) or bleeding disorder
• Subject who is judged to be ineligible according to their physical checkup(medical history, physical examination, ECG, laboratory values and etc.) within 56 days prior to the first administration
• Concomitant use of one or more of nitrates/nitric oxide(NO) donor(e.g. nitroglycerine, isosorbid, mononitrate, isosorbid dinitrate, amylnitrate/nitrite, sodium nitroprusside), Trazodone, cancer chemotherapy, anticoagulants, androgens, or anti-androgens
• Use of any PDE-5 inhibitor(e.g. Viagra, Levitra, Cialis, Yaila, or Zydena), vasodilator self-injection, or other treatments for erectile dysfunction within the last 2 weeks prior to the study
• Participated in any other clinical trials within 30 days prior to the first administration
• Have history of primary hypoactive sexual desire
• Subject who is judged to be ineligible by principal investigator or sub-investigator due to mental disorder or continuous drug abuse