We report the changes in surface state of tri-n-octylphosphine oxide (TOPO) capped CdSe nacocrystals by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). In the photobrightening state, where photoluminescence (PL) intensity increased during the illumination, surface ligand rearrangement such as the TOPO-Se compelx and TOPO dimers; are formed, which might be deeply correlated with the PL enhancement. It was also observed that surface oxidation and decomposition of TOPO, which is followed by the desorption, occurred in photodarkening state.