Second and third order nonlinear optical susceptibilities of A(6)M(2)M(8)O-30 ferroelectric crystallites 100 nm powders were studied. The measurements were carried out for powders and thin films of guest-host composites made of Poly(methyl methacrylate) (PMMA) matrix. The studies were carried out by Kurtz Perry method using a Q-switch 16 ps picosecond Nd:YAG laser with peak pulse power 25 MW operating at 1064 nm fundamental wavelength. We have established that Ba6Ti2Nb8O30 ferroelectric crystallites achieve the highest (among the studied materials) second order optical susceptibilities equal to about 8.12 pm/V. The use of picosecond laser pulses and of the crystallites with high monodispersion allow to obtain an information concerning the second order optical susceptibilities with the avoiding of the local thermoheating which may change the output susceptibilities.