Blends made of one linear low density polyethylene (LLDPE) and either of two low density polyethylenes (LDPE 1 and LDPE 2) were rested in elongational modes of deformation using elongational viscosity and melt strength test. In addition to rheological measurements the melt miscibility of the blends was ascertained by the differential scanning calorimetry (DSC) test on melt quenched samples. From the results, the relation between melt morphology of the blends and their performance under elongation, as well as the influence of molecular structure in particular long chain branching, on elongational response were determined. It was observed that high resistance to elongational deformation of the blends is linked to the immiscibility of the blend components in the melt. On the other hand the influence of long chain branching is to increase elongational viscosity for the parent polymers, as well as promoting the blend immiscibility and therefore altering elongational performance of the blends.