Background: The major goal in postoperative pain management is to minimize the dose of medications and decrease side effects while still providing adequate analgesia. Postoperative pain relief leads to earlier mobilization, shortened hospital staying, reduced hospital costs and increased patient satisfaction.  Aim of the study: To compare the effect of intravenous magnesium sulfate versus intravenous diclofenac on postoperative analgesia in patients undergoing total abdominal hysterectomy.  Patients and Methods: This single blinded randomized controlled clinical study was conducted on 60 patients who had undergone hysterectomy surgery in Ain-Shams University Maternity Hospital from October 2017 to July 2018. The patients were divided into two groups of 30 patients each based on a random number table; one receiving magnesium sulphate and the other receiving diclofenac.  Results: The mean age of the patients in group A was 49.97±5.31 and it was 51.50 ±6.13 in the study group B; there was no significant difference between them (p < 0.05) p=0.305. The mean BMI of the patients in group A was 27.45±2.13 Kg/m2 and it was 27.12±2.42 Kg/m2 in group B i.e., there was no significant difference between them (p < 0.05 p=0.470). Also, the duration of surgery of all the patients was recorded; the mean duration of surgery of group A was 104.77 ± 8.51 and that of group B was 102.90 ± 10.17 with p value = 0.444.  Conclusion: IV preventive doses (low doses) of magnesium sulphate with dosage of 50 mg/kg in 100 mL of normal saline solution alleviate postoperative pain throughout the first day after TAH under balanced general anesthesia significantly and reduce opioid consumption as well.