A uniform and stable inorganic-organic nanocomposite containing single-walled carbon nanotubes（SWNTs） and dodecyl aldehyde（DA） was obtained by ultrasonication method.The dispersant was dropped on a glassy carbon electrode surface for dryness to get a modified electrode（SWNTs-DA/GCE）.Then the amino modified single-stranded probe DNA was covalently immobilized on SWNTs-DA/GCE by a facile amine-aldehyde condensation reaction,from which a novel DNA electrochemical sensor was constructed.The layer by layer assembly process of the biosensor was characterized by cyclic voltammetry and electrochemical impedance spectroscopy using ［Fe（CN）6］3-/4- ions as electroactive probes.The analytical performance of the biosensor was investigated through using methylene blue（MB） as the hybridization indicator,and the results showed that the peak currents of MB on the biosensor had a good linear relationship with logarithm values of the target DNA concentrations（lgCS2） in the range of 1.0×10-15-1.0×10-10 mol/L(r=0.998）.Based on three times of the signal to noise ratio（S/N=3）,the limit of detection was estimated to be 2.0×10-16 mol/L.The selectivity experiments further showed that the complementary sequences,three base mismatched sequences and the non-complementary sequences could be well distinguished by the biosensor.