Background: Arthroscopic knee surgery encompasses a wide range of surgical operations involving the knee, and several analgesic regimens have been studied to determine the ideal analgesic combinations. The kind and duration of surgical intervention influence post-operative pain response, and it is sometimes difficult to determine which analgesic regimen would be optimal for each patient until post-operatively. Objective: The aim of the current study was to assess the effects of perineurally dexamethasone (DXM) addition to bupivacaine (BVC) in adductor canal block (ACB) for post-operative analgesia after knee arthroscopy under spinal anesthesia regarding. Patients and methods: This a randomized controlled double-blinded controlled clinical trial performed at Ain Shams University Hospitals, Cairo, Egypt. Study Period: Six months. Adults undergoing Knee Arthroscopy under Spinal Anaesthesia employing computer-generated codes and opaque sealed envelopes, were randomly divided into 2 groups: Group A (study group): These patients administered ACB with 20ml plain BVC (0.25%) + 8 mg DXM (2ml), Group B (control group): The patients received ACB with 20ml plain BVC (0.25%) + 2 ml of 0.9% saline. Results: A high statistical significant difference (p < 0.001) was found between both groups as regards analgesic duration (time of first call for analgesics) (min). The highest value was reported in group A(study) and group B(control) (241.02±36.15 and 188.49±28.27) respectively, this indicates that that the needs of analgesic in the group B were earlier than in group A. Also, a high statistical significant difference (p < 0.001) was reported in terms of cumulative morphine consumption “mg". The highest value was reported in Group B and Group A 4 (3-4) and 2 (1-2) respectively, this indicates much higher needs of analgesic in the Group B than group A. Conclusion:ACB is an effective post-operative analgesic for knee arthroscopy performed under spinal anesthesia. Nonetheless, combining (8 mg) DXM with (0.25%) BVC in ACB resulted in superior post-operative analgesia and less analgesic usage compared with BVC alone.