This　work　shows　the　electrical　switching　of　the　nonparametric　optical　nonlinearity　of　tungsten　oxide　(WO3-x).　The　sign　and　magnitude　of　the　effective　nonlinear　absorption　coefficient　(beta(eff))　can　be　modulated　via　application　of　an　external　bias.　With　laser　excitation　at　1030　nm,　WO3-x　shows　a　relatively　large　saturable　absorption　(SA)　under　an　applied　voltage　(V-A)　of　-2.5　V,　with　beta(eff)　being　as　large　as　-632　cm　GW(-1),　while　reverse　saturable　absorption　(RSA)　is　found　for　V-A　larger　than　-1.5　V.　The　electrical　switching　of　the　nonlinear　optical　(NLO)　response　is　reproducible　and　durable.　Both　electrostatic　and　electrochemical　dopings　of　WO3-x　occur　during　V-A　variation,　with　SA　resulting　mainly　from　the　electrochemical　doping　(the　intercalation　of　H+　into　the　lattice　of　WO3-x).　The　wavelength-dependent　NLO　performance　of　pristine　WO3-x　is　attributed　to　competition　between　one-photon　absorption　and　two-photon　absorption,　while　the　V-A-derived　NLO　response　is　correlated　with　variation　in　the　band　structure　and　its　population.　These　results　suggest　a　promising　approach　for　the　postsynthesis　modulation　of　the　NLO　response　and　a　potential　device　configuration　for　further　optoelectric　applications.