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The present report describes the synthesis of a hydroxyl terminal PAMAM dendrimer (PAMAM-OH) derivative (PAMSPF). The hydroxyls of PAMAM-OH were attached to S-Methyl-l-cysteine (SMLC) via an acid-labile ester bond, named as β-thiopropionate bond, followed by modification with folic acid (FA) through a polyethylene glycol (PEG) linker. The degrees of attachment of SMLC and FA to the PAMAM-OH backbone were 83.9% and 12.8%, respectively. PAMSPF could condense DNA to form spherical nanoparticles with particle sizes of ˜200 nm and remain stable in the presence of heparin and nuclease. The β-thiopropionate bond in PAMSPF was hydrolyzed completely and the DNA release rate was 95.8 ± 3.3% after incubation under mildly acidic conditions at 37 °C for 3 h. PAMSPF/DNA was less cytotoxic to KB and HepG2 cells and exhibited a higher gene transfection efficiency than native PAMAM/DNA. The uptake assays showed that PAMSPF/DNA entered KB cells within 0.5 h through folate receptor-mediated endocytosis and escaped from endosomes within 2 h. In addition, PAMSPF/DNA displayed long circulation time along with excellent targeting of tumor sites in vivo. These findings demonstrate that PAMSPF is an excellent carrier for safe and effective gene delivery.