Abstract: Purpose: This study was designed to compare the effects of magnesium sulphate vs. clonidine co administered peribulbarly as adjunct to local anesthesia. Patients and methods: The study comprised 60 patients undergoing posterior segment eye surgeries. The patients were then divided randomly into three groups (20 patients in each group) according to the medications they received: Group O (control group): local anesthetic + saline 0.9% (1 ml). Group M: local anesthetic + magnesium sulphate 50 mg (in 1 ml 0.9% saline) Group C: local anesthetic + clonidine 30 mcg (1 ml). The onset and duration of lid and globe akinesia were assessed every 1 minute until maximum blockade and then every 15 minutes after surgery until complete recovery of the block. Postoperative analgesia was assessed by using Visual Analogue Score (VAS) every hour up to 6 hours postoperatively. If the VAS was > 5, injection of diclofenac 75mg intramuscular was done. Results: Patients received magnesium sulphate showed significantly rapid onset of lid and globe akinasia than other groups while patients received clonidine showed significantly prolonged duration of lid and globe akinasia than other groups. First analgesic requirement is significantly delayed in group M and group C in comparison with the control group (group C). There were statistically significant differences between the groups as regard the mean VAS in 1,2,3,4 hours, M group and C group have lower median pain score than Control group (control group). Conclusion: The current study establishes magnesium sulphate as a predictable and safe adjunct to local anesthetic in peribulbar block for rapid onset of anesthesia and clonidine for prolonged duration of anesthesia.