The recent precision measurements of Z0 decay width of LEP/SLC results may allow the existence of a heavy fourth generation neutrino with mass mν4 above ~45 GeV. The fourth generation neutrinos, by non-radiative decay in the early Universe, may yield a detectable diffuse relic neutrinos (νμ and ντ) on the earth with energies around 10–100 MeV. We discuss a possible detection method of the diffuse relic flux. This relic diffuse neutrino flux, if observed, would strongly support the existence of the fourth generation neutrinos.