We have examined the rate of glycolaldehyde oxidation and the current efficiency of products at Pt electrodes modified by Sb, Bi and Ru ad-atoms, using at various amounts of coverage, and investigated whether the aldehyde functional group in glycolaldehyde molecule is selectively oxidized. The -CHO group is oxidized selectively with respect to the -CH2OH group at a Pt electrode modified by Sb and Bi ad-atoms in the oxidation of glycolaldehyde consisting of both aldehyde group (-CHO) and the alcohol group (-CH,OH). Both the oxidation of the -CHO group and the -CH2OH group are enhanced by Ru ad-atoms. Namely, Ru ad-atoms have no selective enhancement effect on the oxidation of glycolaldehyde.