The causes of low back pain on one side may be lumbar muscle strain, urinary stones or upper urinary tract infection, ankylosing spondylitis and so on. 1. Lumbar muscle strain: Usually, patients suffer from lumbar muscle strain due to prolonged standing or heavy loading of the waist, which leads to the symptoms of lumbago on one side. 2. Urinary stones or infections: most of the urinary stones are retained in the urinary tract, causing damage to the urinary epithelium and blockage, at this time, patients with hydronephrosis will cause low back pain symptoms. Upper urinary tract infection patients, the upper urethra, renal pelvis mucosa congestion and edema, resulting in urinary drainage difficulties, this time easy to appear waist pain. 3. Ankylosing spondylitis: this disease often destroys the spine and lumbar intervertebral disc fibrous ring, leading to damage to the spinal peripheral tissues, triggering pain, therefore, the symptoms often appear as the lower back pain or stiffness. There are many other causes of low back pain on one side, if the patient has a side of low back pain, and long-term non-relief should be timely to the hospital to clarify the cause and targeted treatment, so as not to delay the condition.