We investigated the rheological behavior of linear low-density polyethylene (LLDPE)/polylactic acid (PLA) blends in the presence of modified and non-modified silica nanoparticles in extensional flow. Characterization methods were used as Fourier transform infrared spectroscopy, scanning electron microscopy, and rheometric measurements under shear and uniaxial extensional flows. The rheology behavior of LLDPE significantly was changed by the addition of PLA and silica nanoparticles. Extensional results showed that the elongational viscosity of the blends intensified by the incorporation of silica nanoparticles. Strain hardening was observed for LLDPE containing 2 wt.% of the unmodified silica nanoparticles, which disappeared by enhancement of the unmodified silica from 2 to 8 wt.%. Furthermore, elongation thinning was observed for the filled blends at high loading, which was more sensitive to the strain rate by increasing of PLA. Surface modification of silica was demonstrated in different elongational behavior. Indeed, a fracture took place by loading the modified silica nanoparticles in LLDPE; however, the intensity of this behavior dramatically increased for filled blends with a high loading of modified silica. Graphical abstract