Background: Morphine is an opioid and its intrathecal use for postoperative pain relief is well documented. Nausea and vomiting are the common adverse effects with intrathecal morphine and might be distressing in patients undergoing abdominal surgeries limiting its usage. Ondansetron is helpful in treating of nausea and vomiting but would be of greater help when administered pre-emptively. Aims and Objectives: Primary aim of study was to study the effect of pre-emptive ondansetron in controlling intrathecal morphine induced nausea and vomiting. Secondary aims was to assess its effectiveness in controlling pruritus. Methods and Materials: In this prospective, randomized study ninety patients undergoing abdominal hysterectomy were categorized into 3 equal groups receiving 15mg hyperbaric Inj.bupivacaine, in addition 0.5ml saline in Group-I, and 100µg and 200µg of intrathecal morphine diluted to 0.5ml respectively in Group-II and Group-III. All patients received 4mg of Inj.ondansetron intravenously 10 minutes before administering spinal drug preparation. Patients were assessed for duration of analgesia, nausea, vomiting, pruritus and other adverse effects of intrathecal morphine. Results: There was statistical significant difference with respect to age, body mass index and duration of surgery between three groups. Intrathecal morphine resulted in significantly longer duration of analgesia in patients receiving intrathecal morphine (p<0.001). Pre-emptive ondansetron effectively controlled intrathecal morphine induced nausea (p=0.809) and vomiting (p=0.199) and it was statistically insignificant when compared to control group, but did not decrease incidence of pruritus (p=0.027). Conclusion: Pre-emptive intravenous Inj.ondansetron (4mg) effectively controls intrathecal morphine induced nausea and vomiting but not pruritus.