A new type of linear copolymers, poly(ortho ester amino alcohols) (POEAAs), has been synthesized by ring-opening polymerization between diglycidyl ethers and amine monomer with ortho ether bonds. POEAAs have uniform distribution of tertiary amine main-chains along with abundant hydroxyl groups and acid-cleavable tertiary amine side-chains. POEAA1 and 2 containing different diglycidyl ether moieties were prepared to regulate their hydrophilicity and DNA condensation ability. POEAAs could efficiently condense plasmid DNA into nanoparticles, which have much lower cytotoxicity than branched PEI (25 KDa). The breakage of tertiary amines in side chains of POEAAs caused by hydrolysis of ortho ester bonds at mildly acid-pHs could obviously facilitate the release of DNA from the polyplexes. More significantly, the effective transfection on 293T cells mediated by POEAAs was not negatively affected by 10% serum concentration because of their improved serum tolerance. (C) 2016 Elsevier Ltd. All rights reserved.