PROBLEM TO BE SOLVED: To develop technique capable of amplifying cells having high NK cell purity, high NK cell amplification magnification and little commingling of T cells, even from umbilical cord blood and peripheral blood without using feeder cells.SOLUTION: There are provided a composition for amplifying natural killer cells (NK cells) containing one or more kinds of compounds selected from the group consisting of tacrolimus, derivatives and salts thereof, and dalteparin, derivatives and salts thereof； and a method for amplifying the NK cells including a step of preparing the NK cells and a step of incubating the NK cells in the presence of one or more kinds of compounds selected from the group consisting of tacrolimus, derivatives and salts thereof, and dalteparin, derivatives and salts thereof.
