Single-stranded DNA (ssDNA) immobilization in a highly oriented manner with controlled ssDNA density on a gold surface was accomplished by surface modification with our original poly(ethylene glycol) (PEG)-block-oligoamine copolymer, followed by immobilization of thiol-ended ssDNA (ssDNA-SH) on the PEG tethered chain surface. As the length of the polyamine segment in the block copolymer increased, the immobilization amount of ssDNA-SH on the gold surface increased. The constructed surface improved the signal of the hybridization of ssDNA-SH with its target ssDNA, as found by surface plasmon resonance (SPR) measurements.