A hydrogenated butadiene block copolymer (CEBC), polyethylene-poly(ethylene-co-butene)-polyethylene block copolymer, was found to be miscible with high density polyethylene (PE). We investigated the lamellar crystalline structure in the blends crystallized from the single-phase melt by TEM observation and DSC measurement. It is well known that crystal lamella of PE grows rather straight and the edge view of the lamella under TEM is a long stripe. Such lamellar structure was observed in 50/50 PE/CEBC blends crystallized at high temperatures(e.g., 110 degrees C). On the other hand, when the blend was crystallized at low temperatures (e.g., 75 degrees C), the lamella was not straight but zigzag. The difference of the lamellar structure was characterized by two morphological parameters : a persistent lamellar length PLL defined by the length of a straight lamellar segment formed by a persistent growth, and an angle alpha (between two persistent lamellae. The blend crystallized at lower angle alpha between temperatures had shorter PLL and wider alpha. Differential scanning calorimetry melting peak of C (PE) block of CEBC was not detected in the blend crystallized at low T-c, suggesting an incorporation of C block chains in PE lamellae. The incorporation seems to force the zigzag growth of PE lamellae. The shorter the PLL and the wider the value of alpha, the less ordered was the spherulite in radial direction.