Objectives: To compare the pain relief effect between the titration of morphine combined with ketamine and morphine alone in postoperative patients with abdominal surgery. Methods: A randomized controlled clinical mal was conducted on 120 patients alter abdominal surgery who were divided into three groups, each group consisted of 40 patients in Anesthesiology Health Bach Mai Hospital from 3/2010 to 9/2010. Results: Reduce morphine consumption in the 60-minute titration (12.30 + or - 4.99 mg in group II, 12.35 + or - 5.36 mg in group III with 15.35 + or - 5.3 mg in group I), increase the success of titration (92.5 percent in group II, 65 percent in group III compared with 60 percent in group I) and significantly decrease the Petfalgan dose used immediately alter the titration (0.10 + or - 0.30 g in group II, 0.32 + or - 0.47 g in group III compared with 0.35 + or - 0.48 g in group I. Conclusions: Combination of morphine and the low-dose ketamine in the ratio 1:1 has good pain relief effect, redudng the total dose of morphine consumed in the 60-minute titration, thus ina-eases the success of the titration and significantly reduces additive analgesic dose used alter titration and has low side effects.