Objective?To observe the effects of magnesium sulphate on tracheal extubation reaction and postoperative pain in patients undergoing laparoscopic radical surgery for colorectal cancer. ?Methods?60 patients underwent laparoscopic radical surgery were randomly divided into two groups (Group MgSO4 and Group NS), with 30 cases in each. The magnesium group (Group MgSO4) received 50.00 mg/kg of magnesium sulphate in a total of 100 ml normal saline for 15 min before induction of anaesthesia and then 15 mg/(kg?h) by continuous i.v. infusion until the end of surgery. The saline group (Group NS) received the same volume of isotonic saline over the same period. At the end of surgery, all the patients received PCA with Sulfentanyl. MAP and HR were recorded at the following points: preoperative evaluation (T0), the time after induction (T1), the time of sputum suction (T2), the time of extubation (T3), 2 min (T4) and 5 min (T5) after extubation. The VAS scores at rest and during coughing and the consumption of PCIA were recorded at 4 h (T6), 12 h (T7), 24 h (T8) and 36 h (T9) after surgery. The total consumption of Sulfentanyl and Remifentanil, operation time, anesthesia time, operative incision, extubation time, side effects and rescue analgesics such as flurbiprofen axetil were also recorded.?Results?Compared with Group NS, the total consumption of Remifentanil in Group MgSO4 was lower (P < 0.05), but extubation time was longer (P < 0.05). MAP and HR at T1, T2, T3, T4 and T5 in Group NS were higher than those in Group MgSO4 (P < 0.01), and MAP and HR at T2, T3, T4 and T5 in Group NS were higher than those at T0 (P < 0.01), and MAP and HR at T1 in both two groups were lower than those at T0 (P < 0.05). There were no significant differences in the intensity of pain at rest and during coughing and the consumption of PCIA at T6 between two groups (P > 0.05). The intensity of pain at rest and during coughing at T7, T8 and T9 in Group MgSO4 was lower (P < 0.05), and the consumption of PCIA during T6～T7, T7～T8 and T8～T9 in Group MgSO4 was also lower (P < 0.05). Compared with Group NS, the incidence of nausea and vomiting and rescue analgesics in Group MgSO4 was lower (P < 0.05).?Conclusion?Magnesium sulphate could reduce the stress response to tracheal extubation, the postoperative pain, the consumption of PCIA and the incidence of nausea and vomiting in patients undergoing elective laparoscopic radical surgery for colorectal cancer.