This work reports a comprehensive study on poly (Ethylmethacrylate-co-Acrylonitrile) Poly(EMA-AN) nanocomposites reinforced with a hybrid mix-ture of nanoreiforcements based on nanocrystals of cellulose (NCC) (1 or 5% wt) and halloysite nanotubes (HNTs) (1 or 5% wt). The morphology, thermal and mechanical properties of these nanocomposites were characterized. Homogeneous dispersion of the nanofillers has been shown by scanning electron microscopy. A significant increase of the rubbery modulus and glass transition temperature were obtained upon filler addition, due to the reduction of mobility of the matrix macromolecular chains. On the other hand, compared with the neat Poly(EMA-AN), the storage modulus of the nanocomposites increased by a factor 38 when adding 5 wt% NCC and by 17 for the same concentration of HNTs. mechanical properties of ternary nanocomposites were furthers increased resulting from a synergistic effect of these two nanofillers. © 2020, Tech Science Press. All rights reserved.