In the last decades, one of the most critical issues concerning the control on the processing, structure and properties ofnanocomposites is related to the dispersion of nanofiller in the polymer matrix and internal interactions resulting in percolation.In this study, we investigate the rheological behavior in oscillatory and steady shear flow of poly(lactic) acid basednanocomposites incorporating 0 - 12 wt% graphene nanoplates (GNP) and multi-walled carbon natotubes (OH-MWCNT). Theeffect of the filler contents and aspect ratio on the viscosity and viscoelastic response is evaluated. Three rheological techniquesare used for estimation of rheological percolation threshold. Due to different aspect ratio and state of dispersion ofGNP and MWCNTs the percolation threshold differs significantly... for both compositions phi; le; 1.5 wt% for MWCNT/PLAand phi;p le; 5 wt% for GNP/PLA. The larger the aspect ratio of nanofiller, the lower is the rheological percolation threshold. The visualizedstructure by TEM analysis confirms the rheological predictions for both type composites. The index of flow was estimatedby the power law slope of the flow curves and a better dispersion was assumed for MWCNTs in comparison with GNPsdue to the surface modification. Based on the rheological percolation threshold and the flow index, nanocomposites wereclassified in three groups: Newtonian, percolated composites and elastic solids. Both characteristics are used to select theprinting parameters for the three groups of nanocomposites, suitable for fused deposition modeling (FDM).