Antisynthetase syndrome (ASS) is a type of idiopathic inflammatory myopathy (IIM), which is characterized by the presence of antibodies against aminoacyl-tRNA synthetases in serum, and is associated with multiple clinical syndromes. Clinical manifestations, serological indicators, and chest imaging findings differ for different clinical ASS subtypes. The association of myositis and cancer occurrence, in cancer-associated myositis (CAM), is well known. The correlation between myositis, cancer occurrence time, and CAM remission after cancer treatment indicates that in some cases, CAM might be a type of paraneoplastic myositis syndrome. 1 Kaposi sarcoma (KS) is a vasoproliferative disease caused by human herpes virus (HHV)-8 infections, which is associated with human immunodeficiency virus (HIV) infection and immunosuppression. We report the first case of ASS complicated with KS during therapy in China, analyze its clinical characteristics, and review the relevant literature.