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The rare earth metal Gd(III), Yb(III), Lu(III), Eu(III), Tb(III) and Ho(III) complexes 1 – 6 with 2-((2-(pyridin-2-yl)hydrazono)methyl)quinolin-8-ol (H-L) as ligands were synthesized. The in vitro cytotoxicity assay indicated that the cytotoxicity of 1 was equivalent to cisplatin and higher than that of H-L and other complexes towards T24 tumor cells. The mechanism study indicated that 1 caused significant up-regulation of the proteins p27, p21 and p53 in T24 cells and cell cycle arrest in G2 phase. In addition, 1 induced effective T24 cells apoptosis via mitochondrial dysfunction pathway, which was indicated by changes in mitochondrial membrane potential (Δψ), reactive oxygen species (ROS), intracellular Ca2+ and the mitochondria-related proteins (including cytochrome C (Cyt C), B-cell lymphoma-2 (Bcl-2), Bcl-2-associated x (Bax) and apoptotic protease activating factor-1 (Apaf-1)). Moreover, 1 could activate caspase-3/8/9 in T24 cells. Therefore, complex 1 is a promising and potent anticancer drug candidate. Non-anionic-cationic type Gd(III) complex 1 , which exhibited hight cytotoxicity to towards T24 cells and low cytotoxicity towards HL-7702 cells, induced T24 cells arrest in the G2 phase and apoptosis via a mitochondrial dysfunction pathway. Unlabelled Image • Six new rare earth complexes with quinolinyl hydrazine were synthesized. • Complex 1 exhibited selective cytotoxicity to tumor cells versus HL-7702 cells. • Complex 1 caused T24 cell apoptosis via a mitochondrial dysfunction pathway. [ABSTRACT FROM AUTHOR]