The main causes of unilateral ankle swelling are related to joint inflammation, lower limb vascular disease, trauma and tumor. 1. Joint inflammation: if unilateral ankle has local inflammation, such as ankle arthritis, the stimulation of inflammation will easily lead to an increase in inflammatory exudate, which will lead to unilateral ankle swelling symptoms. 2. Lower limb vascular lesions: If one side of the lower limb has vascular lesions, such as varicose veins or deep vein thrombosis, it can directly affect the blood return of the ankle area, thus producing unilateral ankle edema symptoms. 3. Trauma: unilateral ankle injury or sports strain caused by the impact of external forces, the local exudate increases, which triggers localized swelling and may be accompanied by pain. 4. Tumor: If there is tumor growth in the area of unilateral ankle, such as bone tumor, the tumor can easily produce direct occupying effect, which will trigger the performance of unilateral ankle swelling. If unilateral ankle swelling can not be relieved by rest or accompanied by other discomforts, you should consult a doctor in time to find out the cause. And under the guidance of the doctor for standardized treatment, to prevent the later aggravation of the condition.