Background: Magnesium Sulfate has been used along with local anesthetics in different regional blocks and found to be effective in decreasing the time of onset of the block and increasing the duration of the block. Objective: To evaluate the effect of addition of Magnesium Sulfate to Lidocaine on the time of onset of the sensory block, the globe and lid akinesia for peribulbar block in cataract surgeries. Patients and Methods: Sixty patients with American Society of Anesthesiologists physical status I to II (ASA I & II) undergoing cataract surgery under peribulbar block were included in this study. Patients were randomized into two groups 30 patients each: Group I (Control group): patients received a peribulbar block using a mixture of 5ml Lidocaine 2% and 1ml normal saline 0.9% . Group II (magnesium group): patients received a peribulbar block using 5ml Lidocaine 2% and Magnesium Sulfate 10% (50mg) diluted in 1 ml normal saline 0.9%. The onset of loss of corneal sensation, globe and lid akinesia and complications were observed and recorded. Results: Patients received Magnesium Sulfate showed significantly rapid onset of complete loss of corneal sensation (P = 0.036), and significantly rapid onset of partial and complete lid and globe akinesia (P < 0.001) and (P < 0.001) respectively. Conclusion: Addition of 50 mg of Magnesium Sulfate to the Lidocaine for peribulbar block decreases the onset of sensory block and akinesia without any obvious side effect. Keywords: Magnesium Sulfate , Peribulbar Block , Cataract