Adsorption of CTAB and HBr on Pt(100) in acid solutions were studied by using cyclic voltammetry (CV). The effects of bromide anion (Br-), and cetyltrimethylammonium cation (CTA(+)) together with Br- (CTAB) on the long-range ordered structure of Pt(100) were investigated systematically and analyzed quantitatively. It has demonstrated that adsorption of both CTA(+) and Br- can protect the long-range ordered structure of Pt(100). The upper limit potential of CV below which the long-range ordered structure of Pt(100) is starting to be disturbed was measured at 0.6 V in 0.1 M H2SO4, and it was shifted positively to 0.9 V in 0.1 M H2SO4 + 1 mM HBr; this potential has been further postponed to even a higher potential of 1.1 V in 0.1 M H2SO4 + 1 mM CTAB solution, demonstrating that the ability of protecting the long-range ordered structure of Pt(100) is CTAB > HBr. The adsorbed Br- can desorb simultaneously with proton adsorption, while the CTA(+) has adsorbed firmly on Pt(100). It has demonstrated that the irreversibly adsorbed CTA(+) could be mostly removed by CO adsorption/stripping. The results revealed that the origin of protecting the long-range ordered (100) structure by HBr is mainly through the inhibition of oxygen adsorption, while that by CTAB comes from both the inhibition of oxygen adsorption and the CTA(+) irreversible adsorption. The study has thrown insights in understanding the interaction of Br- and CTA(+) with Pt(100), and interpreted that using CTAB as shape-tuning agent is more favorable to yield Pt nanomaterials with long-range ordered (100) surface structure. (C) 2015 Elsevier Ltd. All rights reserved.