Time resolved optical properties of CdSe tetrapod nanocrystals where studied. The results show that the decays of photoluminescence (PL) intensities for tetrapods in solution and on insulating silicon substrate can be well fitted by a bi-exponential function. Based on the emission-energy dependence of carrier lifetimes, the fast and slow PL decays of CdSe tetrapods are attributed to the recombination of delocalized carriers and the localized carriers in the localized states, respectively. By comparing the amplitude ratio of the fast-decay component to the slow-decay component for samples in solution with those on silicon, it is concluded that the slow PL decay is associated with the recombination of localized carriers in the surface defects of CdSe tetrapods.