Development of high-speed DSC instruments made it possible to measure exothermic or endothermic behaviors in hi-speed heating or cooling equivalent to the cooling in high-speed melt spinning process or quenching on the mold surface in injection molding process. Tiny specimen was used for high-speed DSC measurement to decrease thermal distribution in the specimen. Only 1 s was enough to melt polymer and measure crystallization behavior in cooling from molten state in tiny specimen of polyethylene. Total value of exothermic heat by crystallization in cooling was nearly constant despite of previous melting time. However, peak temperature of exothermic heat varied depending on melting time. It means that crystallization behavior was influenced by melting history. In this study, crystallization behavior of high-density polyethylene and liner-low-density polyethylene was measured by high-speed DSC repeatedly in different melting time. In high-density polyethylene, crystallization peak temperature was nearly stable after 20 cycles when the melting time was 2 s. In contrast, crystallization peak temperature decreased 95 degree C to 85 degree C when the melting time was 2 min. In linear-low-density polyethylene, decrease of crystallization peak temperature was smaller than high-density polyethylene even at melting time was 2 min.