Abstract: Third space fluid(TSF) is a common complication of advanced malignancies, including malignant pleural effusion, malignant ascites, intracranial effusion, and pelvic effusion, etc. The pharmacokinetics(PK) of anti-tumor drugs in vivo are influenced by various factors, and TSF is one of the potential factors that contributes to PK variations, which may consequently affect the efficacy and safety of anti-tumor drugs. This paper aimed to comprehensively investigate PK studies related to anti-tumor drugs in patients with malignant tumors accompanied by TSF. The paper summarized the PK characteristics of common cytotoxic drugs, small molecule targeted drugs, and monoclonal antibodies in both blood and TSF.