Objectives: Chronic radicular Low Back Pain is One of The Most Common Cause of Pain Clinic Admission Which is treated with Transforaminal Steroid Injection. Due to Steroid Injection Side Effects, We Decided to Compare Magnesium Sulfate Effects in This Study. Study design: Sample size is 30 patients. Patients with chronic low back pain which fulfill study criteria, randomly assigned into two groups by block randomization. The study will be done double – blinded in one center. Participation: inclusion criteria: radicular pain at least for 6 weeks, MRI findings, VAS>4, age between 20 and 70 years. Exclusion criteria: coagulopathy, local and systematic infections, allergic reaction to drugs, pregnancy, more than 3 pathologic levels and severe scoliosis. Intervention: Patients under local anesthesia and fluoroscopic guidance in prone position in operative room, transforaminal block will be done. In group 1, Ropivacaine 0.2%, 3cc with Triamcinolone 20 mg and in group 2, Ropivacaine 0.2% ,3cc with Magnesium Sulfate 150 mg will be injected. Visual analog scale (VAS), Oswestry disability Index (ODI), analgesic need, straight leg raise (SLR) will be checked as follow: before injection, 2 weeks later first, 3 and 6 months later. Fasting Blood Sugar (FBS) will be checked and Recorded as follow: before injection, 2 weeks later and first month later. Ca, Mg, Vit-C and Vit-D will be checked and Recorded as follow: before and 1 month later. The results will be analyzed and compared.