Biodegradable and lipid-like highly branched poly(β-amino ester)s, HPAESA, were developed to enhance the biological functions of adipose-derived stem cells by gene transfection. Biodegradability reduces the cytotoxicity of HPAESA and enables controlled DNA release. Lipid mimicry enhances cellular uptake and endosomal escape of HPAESA/DNA polyplexes. HPAESA are able to transfect rat adipose-derived stem cells (rADSs) and human ADSCs (hADSCs) with orders of magnitude higher efficiency than commercial gene transfection reagents, with cell viability exceeding 90%. Most importantly, HPAESA can effectively transfer the nerve growth factor (NGF)-encoding plasmid to rADSCs and induce high NGF secretion, which significantly promotes neurite outgrowth of PC12 cells.