Ultrathin films of poly-diallyldimethylammonium chloride (PDDA)/polystyrene sulfonate (PSS) and PDDA/poly(3,4-ethylene dioxythiophene)-polystyrene sulfonate (PEDOT-PSS) were constructed on Ta₂O₅ films through layer-by-layer electrostatic self-assembly (ESA) method for a surface modification purpose. The self-assembly ability of PDDA/PSS and PDDA/PEDOT-PSS ultrathin films on Ta₂O₅ film was investigated. The results showed that the ESA ultrathin films can be constructed on Ta₂O₅ film surface with a layer-by-layer deposition method, and the Ta₂O₅ film covered with ESA film exhibited smoother surface roughness compared with Ta₂O₅ film without surface modification. Moreover, the electronic performance of Ta/Ta₂O₅/ESA films/polymer film capacitor structure was investigated. The results revealed that the capacitor composed of ultrathin ESA film exhibited better anti-voltage endurance ability and less leakage current, which resulted from the isolation of leakage current channel in Ta₂O₅ films because of surface coverage of ultrathin ESA film on Ta₂O₅. It also can be found that the thicker ultrathin ESA film for surface modification resulted in better anti-voltage endurance ability and higher equivalent series resistance (ESR) of Ta₂O₅ capacitor. The further investigation confirmed that lower ESR of capacitor composed of PDDA/PEDOT-PSS ESA films because of high conductive ability of PEDOT-PSS.