Although the earthworm is an important animal species capable of regenerating missing body part, earthworm regeneration is not well understood at the tissue, cell and molecular levels. In order to understand the developmental changes of blastema during earthworm tail regeneration, the formation and development blastema during regeneration was investigated by histological analysis. Within 1 day after amputation, dediffentiating blastemal cells appeared in coelomic side of longitudinal muscle layer. At 3 days postamputation, proliferating blastemal cells migrated into coelum and blastema was formed beneath wound epithelium around 7 days after amputation. Segmentation of blastema was observed around 2 weeks after amputation followed by redifferentiation of nephridium, intestine, setae and septa.