We have studied the chirality effect on the optical nonlinearity of ferroelectric liquid crystals (FLCs) by means of the second-harmonic generation (SHG). A chiral agent of CB15 is added to a commercial FLC of CS1017 for controlling the optical activity in terms of chirality. From the electric-field dependence of the SHG profiles, it is found that the chirality contributes to both the second-order nonlinearity and third-order one which couples with a static electric field.