Objective: Reducing the pain after root canal therapy is a key aspect in endodontic practice. The present systematic review aimed to identify the factors that influence postobturation pain (POP) in patients receiving single-visit nonsurgical root canal treatment. Data Sources: A literature search was performed manually and in Pubmed (Medline) database to identify relevant articles. A data extraction form was constructed and data were collected from the identified articles. Results: In total, 24 articles were identified for the systematic review, and factors associated with POP were tabulated. Conclusion: Specific preoperative factors (old age, sex, molar teeth, mandibular teeth, presence of preoperative pain, and absence of periapical radiolucency) and procedures (administration of prophylactic drug, bupivicaine anesthetic agent, radiograph or apex locator working length determination methods, instrumentation, irrigating system, laser, cold lateral compaction obturation technique, reducing the occlusion, and postoperative drugs) were associated with POP. Keywords: age, gender, postobturation pain, root canal treatment