Very-low-density polyethylenes (VLDPEs) with short branches, formed by metallocene or Ziegler-Natta catalysts, were blended with low-density polyethylenes (LDPEs) or VLDPEs with long branches. The crystallization and melting behavior of these blends were examined by differential scanning calorimetry(DSC). The blends of metallocene-catalyzed VLDPE1 and LDPEs showed a smooth change in both crystallization and melting peak temperatures, indicating that there was co-crystallization and, hence, partial miscibility at all compositions. However, the blends of VLDPE1 and long-chain branched VLDPE2 co-crystallized at 50% or less VLDPE2 content, whereas Ziegler-Natta-catalyzed VLDPE3-VLDPE2 blends showed co-crystallization at 50% or higher VLDPE2 compositions. It is concluded that either complete or partial miscibility has occurred between the two polyethylenes in each of the blends with VLDPE2. Nevertheless, VLDPE2 did not cause a significant change in the morphology of VLDPE1, perhaps because of the reduced number of long branches present in VLDPE2 compared with LDPEs. The molar masses or melt flow indices of the polyethylenes were not significant in controlling the morphology; only the distribution of branches along the chains was important.