Abstract: Arsenic trioxide (ATO) serves as a component of traditional Chinese medicine and a modern anticancer agent, demonstrating remarkable efficacy in the long-term treatment of acute promyelocytic leukemia. With increasing research into its application in solid tumors, ATO's diverse mechanisms of action and potential clinical value have attracted widespread attention. ATO can inhibit tumor cell proliferation by inducing various forms of cell death, such as apoptosis, autophagy, pyroptosis, necroptosis, and ferroptosis, as well as by regulating cell differentiation. Moreover, its modulatory effects on the tumor immune microenvironment provide a new aspectto its antitumor activity. Nevertheless, the clinical application of ATO in solid tumors faces challenges such as low bioavailability, inadequate targeting, and adverse effects. The development of nanocarriers and targeted delivery systems has emerged asa key strategy for enhancing the therapeutic efficacy of ATO. This review systematically summarizes the multiple mechanisms of action of ATO in solid tumors and recent advances in nanodelivery technologies, explores the potential of ATO-based combination therapies, and discusses future directions, aiming to provide a theoretical foundation and practical guidance for the clinical application of ATO in solid tumors.