In this study, the nonlinear response of polymer nanocomposites under large amplitude oscillatory shear (LAOS) flow was investigated. We first investigated polycaprolactone (PCL)/multiwall nanotube (MWNT) composites under LAOS flow using different analyzing methods including Lissajous plot analysis, stress decomposition, and Fourier transform rheology (FT-rheology). The nonlinear parameter Q (equivalent to I-3/1/gamma(2)(0)) was obtained from the FT-rheology as a function of strain amplitude, and the zero-strain nonlinearity Q(0) (equivalent to lim(gamma 0)->(0)Q) was also calculated. We compared the linear and nonlinear viscoelastic properties as we increase MWNT concentration (phi). It was found that the zero-strain nonlinearity (Q(0)) was more sensitive to detect the effect of MWNT concentration than the linear viscoelastic properties. We also investigated the effect of particle shape on nonlinear viscoelastic properties of the polymer composites containing particles of different shape, e.g., PCL/MWNT (one-dimensional thread shape), PCL/organomodified montmorillonite (two-dimensional plate shape), PCL/precipitated calcium carbonate (three-dimensional cubic shape). Furthermore, we introduced a new parameter, nonlinear-linear viscoelastic ratio, to compare linear and nonlinear viscoelasticity. (C) 2013 The Society of Rheology. [http://dx.doi.org/10.1122/1.4795748]