Surface　terminations　of　two-dimensional　materials　should　have　a　strong　influence　on　the　nonlinear　optical　(NLO)　properties,　but　the　relationship　between　surface　terminations　and　NLO　properties　has　not　yet　been　reported.　In　this　work,　switching　the　NLO　properties　of　MXenes　(Ti3C2Tx)　via　＂surface　terminations　modulation＂　is　explored.　The　surface　terminations　of　Ti3C2Tx　are　modulated　by　electrochemical　treatment,　resulting　in　different　states　(viz.,　Ti3C2Tx(pristine),　Ti3C2Tx(=O　rich),　and　Ti3C2Tx(-OH　rich)).　The　sign　and　magnitude　of　the　effective　NLO　absorption　coefficient　(Weff)　change　with　the　surface　terminations.　Ti3C2Tx(=O　rich)　shows　a　relatively　large　saturable　absorption　(SA)　with　laser　excitation　at　515　nm　(Weff　=　-1020　+/-　136.2　cm　GW-1),　while　reverse　saturable　absorption　(RSA)　is　found　in　Ti3C2Tx(pristine)　and　Ti3C2Tx(-OH　rich).　The　RSA　of　Ti3C2Tx(pristine)　and　Ti3C2Tx(-OH　rich)　is　attributed　to　excited-state　absorption,　while　the　SA　of　Ti3C2Tx(=O　rich)　is　associated　with　Pauli　blocking.　With　laser　excitation　at　800　nm,　the　Weff　of　Ti3C2Tx(-OH　rich)　is　113　+/-　3.2　cm　GW-1,　1.68　times　that　of　Ti3C2Tx(pristine);　the　RSA　is　caused　by　photon-induced　absorption.　Our　results　reveal　a　correlation　between　surface　terminations　and　NLO　properties,　highlighting　the　potential　of　MXenes　in　photoelectronics.