To ascertain the principal active peroxynitrite ($ONOO^-$) scavenging components of heat-processed Panax ginseng C.A. Meyer (sun ginseng [SG]), the $ONOO^-$ scavenging activities of fractions and components of SG were compared. The results demonstrated that the $ONOO^-$ scavenging ability of SG was due to its ether fraction containing phenolic compounds. High-performance liquid chromatography analysis and $ONOO^-$ scavenging activity tests of the phenolic acids contained in SG identified vanillic acid, ferulic acid, p-coumaric acid, syringic acid, and maltol as the main active $ONOO^-$ scavenging components of SG. The $ONOO^-$ scavenging activities of phenolic acids and maltol were dependent on the degrees of their proton donating ability.