A novel oligonucleotide carrier which can scavenge ROS is described. The synthesized graft polymer is composed of a PEG segment and a TEMPO-containing hydrophobic segment for scavenging ROS. This graft polymer can form a PIC through electrostatic interaction with oligonucleotides such as siRNA. The amount of ROS was monitored by fluorescence measurements using H2DCFDA as a probe, and it was confirmed that the ROS level was effectively suppressed. The cellular uptake of PIC containing the fluorescence-labeled oligonucleotide was evaluated by fluorescence microscopy. Delivered siRNA suppressed the expression of the mRNA. The prepared graft copolymer is thus a promising candidate as a novel oligonucleotide carrier which also reduces ROS damage generated by cationic polymer carriers.