Autoimmune connective tissue diseases (ACTDs) affect many organs in the body. The presence of antinuclear autoantibodies (ANAs) is considered as the gold standard in the diagnosis of autoimmune connective tissue diseases. Objective: The aim of this study was to use indirect immunofluorescence on Hep - 2 cells (IIF) method to identify the presence of antinuclear autoantibodies in sera of patients with ACTDs in Vietnam National Hospital of Dermatology and Venereology. The result showed that ANAs were present in 39 patient with ACTDs (97.5 percent). The ANA patterns were: Nuclear speckled (38,46 percent), nuclear specked and cytoplasmic (20.51 percent), nuclear speckled and nuclear homogenoU6 (17.95 percent), speckled - nucleolar (2.56 percent), homogenous - discrete speckled (2.56 percent). Detection o.f ANAs by IIF can be a valuable tool for the diagnosis of ACTDs.