Nanocomposites of low density polyethylene (LDPE)/C-18 modified multi wall carbon nanotubes (C-18-CNT) were prepared by melt blending. The effect of C-18-CNT loading and compatibilizer (maleic anhydride modified polyethylene, MAPE) on the morphology, mechanical, thermal and rheological properties of LDPE was studied. FE-SEM images of nano-composites show reduced agglomeration of the in LDPE/C-18-CNT in comparison with uncompatibilized C-18-CNT. For uncompatibilized nanocomposites, yield strength and Young's modulus increased with loading of C-18-CNT. Ultimate strength, show improvement up to 2 wt% loading. However, percent elongation and toughness were reduced for C-18-CNT at all loadings. Apart from elongation and toughness, addition of compatibilizer improved all mechanical properties as compared to pure LDPE and nanocomposites without compatibilizer. Percent crystallinity shows a correlation with Young's modulus. Both, Young's modulus and total crystallinity increased with C-18-CNT loading and further increase with the incorporation of compatibilizer was observed. Results of phase angle suggest no presence of network. Also, addition of C-18-CNT did not increase strain hardening, maintained extensional viscosity and time of break up to 1.5 s(-1) Hencky rate. The C-18 modifier is viewed to act similar to a long chain branching on linear polymers. The C-18 modification of CNT resulted in reduced viscous and elastic properties of the composites. In turn, this is expected to lead to enhancement in the processing of these composites. Overall, compatibilized C-18-CNT resulted in improved mechanical properties and better processing behavior.