Nanocomposite films based on low-density polyethylene (LDPE) containing carvacrol were prepared and characterized with the aim to get antimicrobial active packaging. Organo-modified montmorillonite (MMT) was used as filler. The weak interaction between LDPE and clay led to the formation of intercalated systems. On the other hand, strong interaction between carvacrol and organosilicate allowed a good dispersion of the oil into the clay galleries, promoting the swelling of MMT stacks and a higher polymer/clay interface. As a result, carvacrol was protected against thermal degradation and its release from the films was efficiently delayed. Moreover, outstanding thermal oxidative stability as well as improved oxygen barrier properties were detected in the nanocomposite containing carvacrol. The presence of clay and carvacrol also increased LDPE crystallinity, due to an enhanced nucleation activity, while the mechanical properties of the films were slightly affected. The antimicrobial properties of carvacrol containing films were tested, showing a significant activity against several bacterial strains, which is preserved in presence of the clay. POLYM. ENG. SCI., 49:1447-1455, 2009. (C) 2009 Society of Plastics Engineers