The aim of this study is to determine the properties of cross-linked low density polyethylene (LDPE)/OctaIsobutyl functionalized Polyhedral oligomeric silsesquioxanes (OibPOSS) nanoparticles. The peroxide used in crosslinking is tert-butyl cumyl peroxide (BCUP). The peroxide content was varied as 0.5, 1, 2 and 3 phr. LDPE/OibPOSS/Peroxide nanocomposites were processed in an Xplore Instruments micro-compounder at a screw speed of 50 rpm and 135 deg.C barrel temperature. The crosslinking was carried out using a hot-press operated at 175 deg.C. The LDPE/OibPOSS/Peroxide nanocomposites were characterized by performing tensile tests, differential scanning calorimetry (DSC), rheometer, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Rheological analysis results showed that the degree of cross-linking and storage and loss modules increased with peroxide concentration. According to tensile tests results, tensile strength of composites increased with increasing peroxide content. OibPOSS distribution was investigated by SEM analysis. The incorporation of POSS enhanced ductility of the crosslinked polyethylene. Keywords: Low density polyethylene, Peroxide crosslinked polyethylene, Nanocomposite, Rheology Acknowledgement: This study has been financially supported by TUBITAK (Grant Number: 116M981).