  We study the possibility that the dilaton plays the role of the dark matter
of the universe. We find that the condition for the dilaton to be the dark
matter of the universe strongly restricts its mass to be around 0.5 keV or 270
MeV. For the other mass ranges, the dilaton either undercloses or overcloses
the universe. The 0.5 keV dilaton has the free-streaming distance of about 1.4
Mpc and becomes an excellent candidate of a warm dark matter, while the 270 MeV
one has the free-streaming distance of about 7.4 pc and becomes a cold dark
matter. We discuss the possible ways to detect the dilaton experimentally.
