It is an object of the present invention to provide a composition comprising, as an active ingredient, a pharmacologically elective extract of Ashwagandha leaves obtained without the use of an organic solvent, and a method for producing the same. Such object is attained by providing a composition for inhibiting or preventing aging, treating or preventing tumor or cancer, promoting the proliferation of normal cells or prolonging the life of the same, inducing the proteasomal activity of normal cells, protecting normal cells from stress caused by oxidation or UV irradiation, killing cancer cells or tumor cells or inhibiting the proliferation of the same, or increasing the sensitivity of cancer cells to an anticancer agent which comprises, as an active ingredient, a water extract of Ashwagandha leaves, and a method for producing such composition comprising: a step of adding Ashwagandha leaves to water and treating the same at 20°C to 70°C for 6 to 100 hours； or a step of adding Ashwagandha leaves to water, heating the mixture to 70°C to 100°C, and then letting the resultant cool to 1°C to 30°C.
