The causes of pain in the left side of the lower abdomen are ureteral stones, tumors, inflammation, reproductive system diseases and so on. 1. Ureteral stones: left ureteral stones can cause pain in the left side of the abdomen, usually accompanied by frequent urination, urinary urgency, urinary pain symptoms. 2. Tumor, inflammation: Sigmoid colon, rectal tumor or inflammation can cause left-sided abdominal pain, which may be accompanied by diarrhea, constipation, blood in stool and other symptoms. 3. Reproductive system diseases: men’s left spermatic cord, testicles and epididymis of some diseases, such as inflammation, may cause the left side of the abdomen pain, women’s left ovarian lesions such as tumors, cysts and so on can lead to the left side of the abdomen pain. The pain in the left side of the abdomen need to consult a doctor in time, complete the relevant examination, clear the cause of the disease, active treatment, so as not to delay the condition.