This study investigates the influence of various nanofillers of different shapes and sizes on the properties of PET nanocomposites. PET was reinforced with 0.3 wt.% of different nanoreinforcements, namely: (i) 1D platelet-like shape of organo-modified layered silicates (montmorillonite) (platelet size approx. 1 x 200 nm) with average agglomerate size of: (a) 30 μm and (b) 8 μm; (ii) 3D spherical shape particles of titanium oxide with an average size of 21 nm and (iii) 3D spherical shape silica with an average particle size of 12 nm. PET nanocomposites were prepared by melt blending in an asymmetric batch minimixer followed by compression moulding process. The effect of nanofillers upon thermal, mechanical and structural properties in comparison to the neat PET are discussed.