Percolation thresholds of multiwalled carbon nanotube/polystyrene (MWCNT/PS) nanocomposites (NC) were determined by rheology and electrical conductivity. The percolation threshold found by electrical conductivity was 0.5% carbon nanotubes (CNT) and that by mechanical spectroscopy and relaxation measurements was 0.9% CNT. These results together with those reported in the literature show several types of percolation thresholds, depending on the average fillerfiller (CNT and/or aggregates) distance in a polymer matrix. A distance close to polymer gyration radius corresponds to a soft rheological threshold (PC rheosoft). Close contacts between fillers giving rise to a conductive path corresponds to an electrical threshold (PC elec). At high filler concentration, fillers form a network, corresponding to a rigid rheological threshold (PC rheorigid). These thresholds depend on the filler content and follow the order: PC elecsoft < PC elec < PC rheorigid. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers