Present status and future perspective of experimental tests of time reversal violation using very low energy neutrons are presented.Possibilities to produce high intensity ultra cold neutrons for the measurement of the electric dipole moment (EDM) are shown. Neutron EDM measurements by means of neutron-optical effect in crystals are proposed in ILL and JAERI.Enhancement of parity-violating effect in slow neutron resonance absorption processes encourages us to measure time reversal violation using polarized neutrons on a polarized neucleus.