Cationic polymers have emerged as appealing nonviral gene vectors for decades, which, however, suffer from the paradox between low molecular weight and high transfection efficacy. Low molecular weight cationic polymers (LCPs) are well cell tolerated but are perplexed by orders-of-magnitude less efficacy compared to their macromolecular counterparts. The deficiency mainly lies in weak DNA binding of polymers and difficulty in endosomal escape of formulated polyplexes. Herein, we demonstrate that, through zinc (Zn) coordinated modification of LCPs, the high transfection efficiency and low molecular weight (thus low cytotoxicity) can be achieved simultaneously. The Zn coordinated ligand shows a high affinity to phosphate components and therefore will largely benefit the DNA packaging and endosomal membrane destabilization, addressing the defects of LCPs in gene delivery. Zn coordinative functionalization of LCPs breaks up the "efficacy toxicity" paradox and provides great promise for the development of clinically efficient and safe nonviral gene vectors.