Introduction: Delivering oral hygiene instruction is one of the integral parts of orthodontic treatment. However, there is scarce information regarding the impact of audiovisual method on knowledge retention among orthodontic patients. This study aimed to assess knowledge retention of the patient after instruction delivered in audiovisual (AV) method and compare it to the standard written and verbal (WV) method. Methods: This prospective clinical trial was conducted on 60 patients aged 13 to 40 years. They were randomized into the audiovisual group (n=30) and written & verbal group (n=30). Patients’ knowledge retention was measured using a self-administered questionnaire in Google form, immediately after instruction given as short-term retention and long-term retention for three timepoint, i.e., 1-month, 3-month, and 6-month. Results: There was a significant improvement in knowledge for both AV and WV methods at immediate and 1-month assessment and the knowledge retained until 6-month follow up. The AV method demonstrated a significantly higher increase in knowledge retention at immediate and 1-month than the WV method. Conclusion: The AV method was significantly more effective in improving patient's knowledge retention compared to the written & verbal methods. Repetition of instruction also influence the retention of knowledge.