Unilateral painful submandibular lymph node swelling is caused by oral inflammation in most cases, and local malignant tumors or metastatic tumors can also be caused. 1. Oral inflammation: inflammation of the sublingual gland on the same side, periodontitis and tonsillitis and other inflammatory stimuli can cause unilateral submandibular lymph node enlargement, pain and other symptoms. This kind of inflammation is mostly aseptic inflammatory reaction stimulating the unilateral submandibular lymph node enlargement on the same side and then pain and other symptoms, generally oral non-steroidal anti-inflammatory drugs such as acetaminophen or auxiliary metronidazole tablets, etc. can improve the symptoms. 2. Local malignant tumors or metastatic tumors: for oral malignant tumors or part of breast or lung malignant tumors with ipsilateral lymphatic system metastasis, there can be individual unilateral submandibular lymph node enlargement with pain symptoms. However, this type of situation is relatively rare. Therefore, when unilateral painful submandibular lymph node enlargement, we should consult the hospital as soon as possible to clarify the condition and carry out appropriate treatment.