We investigated the effect of chain length on the cytotoxicity and endocytosis of rhodamine B end-labeled cationic linear poly(2-(N,N-dimethylamino)ethyl methacrylate) (RhB-PDMAEMA) polymers [M-w = (1.1-4.8) x 10(4) g/mol and M-w/M-n similar to 1.2], which were synthesized via atom transfer radical polymerization by using rhodamine B-based initiator. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), lactate dehydrogenase (LDH), and caspase-3/7 assays revealed that the cytotoxicity and cellular membrane disruption of HepG2 cells induced by PD/vIAEMA depend on both the polymer concentration and chain length, and the apoptosis depends on chain length at the concentration of 37.6 mu g/mL. In the concentration range 10-110 mu g/mL, PDMAEMA chains with different lengths are cytotoxic to HepC2 cells by different mechanisms. Namely, (1) for short PDMAEMA chains [M = (1.1-1.7) x 10(4) g/mol] the cytotoxicity, membrane disruption, and apoptosis are very low, independent of the chain length; (2) in the medium range (1.7 X 10(4) < M-w < 3.9 x 10(4) g/mol), the cytotoxicity increases with the chain length and polymer concentration, mainly due to the cooperative effect of membrane disruption and apoptosis; and (3) for long chains [M-w = (3.9-4.8) x 10(4) g/mol], they are very disruptive to the cellular membrane, pro-apoptotic, and able to enter the cytoplasm and nucleus faster than short chains, as revealed by the real-time confocal laser scanning microscopy images, and their much higher cytotoxicity is independent of the PDMAEMA chain length.