The rote of surface spins in the relaxation of magnetization in optically excited Fe3O4 nanocrystals has been investigated via time-resolved Faraday rotation measurements. The time scale of the magnetization recovery following the optically induced demagnetization increased from 250 to 350 ps as the size of the nanocrystals increased from 5 to 15 nm. From analysis of the data with a simple model. relating the spin-lattice relaxation rate to the average spin-orbit coupling strength of the interior and surface spins, we estimated the relative efficiency of surface in spin-lattice relaxation with respect to the interior spins. Our analysis indicates that, in Fe3O4 nanocrystals passivated with oleic acid, the surface is 3 times more efficient in spin-lattice relaxation than the interior.