Objective To investigate the effect of low-dose intraperitoneal ketamine administration on acute MIS in mouse. Methods Thirty-two male C57 / BL6 mice were randomly divided into 4 groups (n = 8): control group (group C), morphine group (group M), ketamine treatment group (K group), ketamine group (KC). Group C and Group M intrathecal of 5μL saline or morphine (1nmol), K group intrathecal of morphine 5 minutes after intraperitoneal injection of ketamine (5mg / mL), KC group intraperitoneal injection of ketamine (5mg / mL).Observation 40 minutes and record hindpaw scratching behavior every 5 minutes. Results Compared with group C, the mice in group M had significantly increased number of scratching bouts, 0-5 minutes (5.00 ± 1.20) mice began to scratching , 6-10 minutes (13.13 ± 1.89) scratching bouts reached its peak, and then decreased, which lasted about 40 minutes; compared with group M, group K scratching bouts in 6-10 minutes (4.75 ± 1.39), 11-15 minutes (4.13 ± 1.25), 16-20 (2.25 ± 0.71) minutes were decline approach the statistical difference(P <0.05), while after intraperitoneal injection of ketamine，total number of bouts were significant decreased in groups K(P <0.05). compared with group KC,group K scraching bouts were approach the statistical difference except 31-40 minutes; while after intraperitoneal injection of ketamine，total number of bouts were significant decreased in groups K(P <0.05); Conclusion Intraperitoneal injection of low-doses of ketamine relieving morphine-induced scratching to a certain extent.