We investigated the frequency upconversion (UC) process in BaTiO3:Er3+ nanocrystals for excitation wavelengths in the range 638 to 660 nm. Green upconversion emissions at 526 and 547 nm corresponding to 2H11/2 --> 4I15/2 and 4S3/2 --> 4I15/2 to transitions of the Er3+ were observed. The excitation spectrum for UC emissions presented three bands, due to ground state and excited state absorption of Er3+ ions. The UC intensity as a function of the laser power was investigated and it was found this a two-photon absorption process.