Doxorubicin (DOX) is an anthraquinone drug used for the efficient treatment of a variety of tumors in human beings. Unfortunately, its poor biodegradability causes incomplete metabolism in the body. Therefore, it is of great significance to synthesize a sensitive and selective material for DOX detection. In this paper, we report a water-soluble Tb12 cluster and track its step-by-step formation (L → Tb1L1 → Tb2L1 → Tb2L2 → Tb3L2 → Tb4L2 → Tb12L6). Tb12 can be used to determine the presence of DOX, which quenches the luminescence of the Tb12 aqueous solution, and the detection limit can reach 13 nM (KSV = 8.7 × 105 M-1). Tb12 has advantages of high sensitivity and high selectivity for the detection of DOX in a simulated environment of human urine and serum.