Branched polyethylenes, low-density polyethylenes (LDPE1 and LDPE2) or long-chain-branched very low density polyethylenes (VLDPE2), were blended with very low density polyethylenes containing short branches (VLDPE1 and VLDPE3). The rheological and thermal measurements of the pure copolymers and their blends (VLDPE1-LDPE1, VLDPE1-LDPE2, VLDPE1-VLDPE2, and VLDPE2-VLDPE3) were taken by controlled stress rheometry and differential scanning calorimetry, respectively. The shear-thinning effect became stronger with increasing long-chain-branched polymer compositions when it was correlated with the flow behavior index, and the extent of shear thinning was different for each blend set. Stronger shear thinning and a linear composition dependence of the zero-shear viscosity were observed for the VLDPE1-LDPE1 and VLDPE1-LDPE2 blends. These blends followed the log additivity rule, and this indicated that they were miscible in the melt at all compositions. In contrast, a deviation from the log additivity rule was observed for the VLDPE1-VLDPE2 blend compositions with 50% or less VLDPE2 and for the VLDPE3-VLDPE2 blends with 50% or more VLDPE2. The thermal properties of the blends were consistent with the rheological properties. VLDPE1-LDPE1 and VLDPE1-LDPE2 showed that these blends were characteristic of a single-component system at all compositions, whereas the phase separation (immiscibility) was detected only for VLDPE1-VLDPE2 blends with 50% or less VLDPE2 and for VLDPE3-VLDPE2 blends with 50% or more VLDPE2. (C) 2005 Wiley Periodicals, Inc.