Approximately 50% of lymphocytic cells derived from peripheral blood is occupied by naive T cells before an activation culture is performed, but the ratio decreases through the activation culture. The occupancy of the memory T cells, which is less than half before the start of the culture, is increased by an activation culture to reach 95%, but decreases if the culture continues. An object of the present invention is to prepare CD45RO positive memory T cell groups in quantity without having to use an antibody or the like, conveniently, and rapidly, and to provide a pharmaceutical composition consisting mainly of the memory T cell groups prepared by the method. According to the present invention, harvested lymphocytic cells are activation-cultured, and the occupancy of the memory T cells in the lymphocyte cell group reaching a desired value is detected through the index of the density of the cultured lymphocyte cell group exceeding a predetermined threshold, the related cell group is harvested for free preservation, and the related free-preserved cell is thawed, cultured, and grown so as to produce the lymphocyte cell groups consisting mainly of the memory T cells in quantity.
