The aim of this study is adding the magnesium sulfate to pain reduction . We assessed the efficacy with VAS. After the approval of ethical committee of University, we obtained a written consent from the patients in a day before surgery. We trained the patients about how to use the visual analogue scale (VAS) . We used the general anesthesia in all patients. We used the same premedication (midazolam 2-3 mg and 1-2 micro/kg Fentanyl ) and induction ( 1/5-2 mg/kg propofol and ./5mg/kg atracurium ) . After that we use the propofol infusion . After the patient interance to recovery room , The patients were randomly assigned to two groups: case group ( magnesium sulfate) and control group . We used the PCIA for all patients . In group 1 ( 40 patients) we infused 30mg/kg sulfate magnesium in 250 cc sodium chloride (over 10 minute) and then 10 mg/kg for 48 hours. We add the above drugs to fentanyl pump . In control group (40 patients) we infused the 250cc sodium chroride over 10 minutes and then the equal volume of magnesium sulfate were infused. We evaluated the heart rate (HR), mean arterial pressure (MAP) and arterial oxygen saturation during the first 6 hours every 2 hours, then 6, 12 , 18 , 24 and 48 after that . Inclusion criteria : patients with the age group of 20 to 50 years؛ patients with ASA I, II , orthopedic surgery will be done under the same procedure with General anesthesia and the surgical team are the same . Exclusion criteria : Patients who have major disease of liver؛ kidney؛ cardiovascular؛ asthma and COPD ؛ patients were treated with calcium channel blocker. In patient with VAS > 4 and continuous and persistent pain, additional 50 micro fentanyl are to be considered. VAS and drug prescribed will be recorded at this time. The patient's pain have been assessed with visual analogue scale (VAS) and will be recorded at 1 , 6 , 12 , 18 , 24 and 48 hours. The patient,s sedation have been assessed with ramsay sedation score in 1 , 6 , 12 , 18 , 24 and 48 hours. We will have evaluated the magnesium serum level at 12 and 24 hours. Anesthesiologist who is not aware of the patient group is responsible for the assessment of the amount of sedation, pain , fentanyl consumption and hemodynamic variables. Side effects such as hypotension (SBP < 100 mmhg) , heart rate <60 b/min, nausea and vomiting have been recorded.