Accurate quantification of cisplatin (cDDP) in body fluids (blood, urine, and ascites) is crucial in monitoring therapeutic processes, assessing drug metabolism, and optimizing treatment schedules for cancer patients. Nonetheless, due to the inherent fluorescence and complexity of the body fluid matrix, along with the low cDDP concentrations in these fluids during treatment, using fluorescent sensors for fluid detection remains a subject of ongoing research. Herein, a series of water-soluble cDDP-activatable fluorescent sensors was rationally constructed by introducing thioether groups to the xanthene skeleton based on the chalcogenophilicity of platinum. These sensors exhibit excellent sensitivity and certain anti-interference capabilities for sensing cDDP in living cells, rat tissues, and zebrafish. Especially, with a simplified sample pretreatment procedure, for the first time, Rh3 and Rh4 have enabled quantitative detection of cDDP levels in diversiform body fluids from clinical ovarian and bladder cancer patients. These results are highly consistent with those obtained by ICP-MS detection. This work paves the way for utilizing fluorescent sensors in clinical body fluid analysis, thus potentially revolutionizing the monitoring methods of cDDP in clinic settings.