Cutaneous squamous cell carcinoma (cSCC) is a common malignant skin neoplasm for which current therapeutic options for advanced and metastatic cases remain limited and are associated with considerable toxicity. Plasma-activated solution (PAS)—prepared by exposing media such as culture medium, water, or phosphate-buffered saline (PBS) to cold atmospheric plasma (CAP)—has emerged as a novel antitumor strategy. In recent years, PAS has garnered increasing attention owing to its advantages over direct CAP application, including ease of storage and clinical administration. In the present study, we investigated the therapeutic potential of PAS in cSCC. In this study, we established an in vitro skin cancer model treated with PAS, as well as an in vivo xenograft tumor model. In vivo experiments demonstrated that PAS significantly suppressed xenograft tumor growth, as evidenced by reductions in both tumor volume and weight, along with a decreased number of Ki-67-positive proliferating cells, without inducing body weight loss or organ damage in treated mice. These antitumor effects were associated with upregulation of the pro-apoptotic protein Bax, downregulation of the anti-apoptotic protein Bcl-2, and suppression of Matrix metalloproteinase-9 (MMP9) expression. In vitro assays revealed that PAS elevated intracellular reactive oxygen species (ROS) levels and induced mitochondrial dysfunction, while modulating the expression of apoptosis-related proteins (Bax/Bcl-2) and the migration-associated molecule MMP9. These effects were consistently validated in two squamous cell carcinoma cell lines, HSC-1 and SCL-1. The activation of the NF-κB signaling pathway and subsequent upregulation of pro-inflammatory cytokine expression were also detected in PAS-treated cells. PAS treatment led to tumor cell apoptosis in a time-dependent manner, rather than inducing significant cell cycle arrest. Collectively, PAS exhibits potent antitumor activity without appreciable systemic toxicity. Our findings provide a promising therapeutic approach for cSCC and suggest PAS as a potential strategy for the treatment of other solid tumors.