It is not possible to generalize whether positive anti-U1-RNP antibodies are serious. Positive anti-U1-RNP antibody suggests mixed connective tissue disease (MCTD). If there are no serious complications, the prognosis of MCTD is relatively good, but the accompanying pulmonary hypertension sometimes progresses rapidly and can be life-threatening in severe cases. Anti-U1-RNP antibody is also known as anti-U1-SnRNP antibody. Positive U1RNP antibody is the most important indicator for the diagnosis of MCTD. Cardiac complications and progressive pulmonary hypertension are the main causes of death in patients with MCTD, and the prognosis is relatively good if the disease is under control with early intervention and active treatment. Symptoms can be controlled clinically with calcium channel antagonists such as nifedipine and angiotensin-converting enzyme inhibitors such as captopril, as well as glucocorticoids such as prednisone and immunosuppressants such as cyclophosphamide and methotrexate. Overall, although the course of MCTD is unpredictable, the prognosis of most patients is relatively good, with a five-year survival rate of more than 90%, which is mainly related to early diagnosis and early treatment. It is recommended that patients go to the hospital for further examination and early symptomatic treatment with the examination results.