The properties of polyethyleneimine-cholesterol cationic lipopolymer (PEI-Chol) as gene carries and its gene transfer efficiency in vitro with lipid microbubbles were presented in this paper.  PEI-Chol lipopolymer was synthesized by linking cholesterol chloroformate to the amino groups of branched poly(ethyleneimine) (PEI) of 1 800.  The structure and molecular weight of PEI-Chol were confirmed by IR, ¹H NMR and MADI-TOF-MS (matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry), respectively.  The average molecular weight of PEI-Chol was approximately 2 000.  The gene delivery system of bubble/PEI-Chol/DNA was constructed by mixed PEI-Chol/pDNA (N/P 10∶1) complexes with lipid microbubbles (2−8 μm) which were  prepared by DPPC, DSPE-PEG₂₀₀₀ and perfluoropropane with the reverse phase evaporation technique.  pEGFP-Cl (enhanced green fluorescent protein) was used as report gene to investigate the DNA condensing ability of PEI-Chol lipopolymer by agarose gel electrophoresis.  And their cytotoxicity and in vitro transfer efficiency of different complexes were compared with each other in A549 and MCF-7.  The results indicated PEI-Chol lipopolymer can condense plasmid DNA when N/P ratio upto 4, PEI-Chol complexes and bubble/PEI-Chol/DNA complexes were nontoxic to A549 and MCF-7 when formulated at the N/P ratio of 10/1 as determined by MTT assay.  This bubble/PEI-Chol/DNA delivery system provided good transfer efficiency with other desirable  characteristics such as against-precipitation of plasma proteins.  In conclusion, bubble/PEI-Chol/DNA complex is a novel non-viral gene delivery system.