Abstract: Surface structure of the glassy carbon surface modified with cobalt tetraphenyl-porphyrin (CoTPP) by thermal-treatment has been studied by XPS, DTA and TG. During the thermal treatment a bond can be formed between the glassy carbon sur-face and TPP. Therefore the stability of electrode for the catalysis of dioxygen redu-ction is improved. Upon thermal treatment at 600 ℃, FWHM of Co(2p_(3/2)) is broa-dened, the reason is due to overlapping of peaks of multiple states; the spin orbit separation between Co(2p_(1/2)) and Co(2p_(3/2)) increases to 15.5—16.3 eV, which indicates a change from low spin divalent to high spin divalent states; the kinetic energy of Co L_3VV Auger line and Auger parameter also increase. These changes of central cobalt ion provide a suitable redox potential for Co(III)/Co(II) which is related to the activity for catalysis of dioxygen reduction.