Rh gets close attention recently since it might improve C1 pathway efficiency toward ethanol oxidation reaction. Considering COad species are the vital intermediates for the C1 pathway, thus we fundamentally investigate the CO adsorption and oxidation on Rh surface. The results show that the formation of COad layer on Rh is more sluggish in alkaline media, may be due to the high OH- concentration induced bigger electronegativity of Rh electrode. This local environment change also leads to the onset potential of COML oxidation in 0.1 M NaOH negatively shift about 200 mV (at ca. 0.43 V) with respect to that in 0.1 M H2SO4. The oxidation of COML on Rh in alkaline media might be divided into two potential sections. One may follow the Eley-Rideal mechanism at 0.45-0.55 V with OH- ions directly attracting the surface weakly adsorbed COL species; the other is the oxidation of COML species through the Langmuir-Hinshelwood mechanism. This work may provide some fundamental supporting for fabricating highly efficient ethanol oxidation catalysts.