  Systematical doping studies have been carried out to search for the possible
superconductivity in the transition metal doped Zr$_5$Ge$_3$ system.
Superconductivity up to 5.7K is discovered in the Ru-doped
Zr$_5$Ge$_{2.5}$Ru$_{0.5}$ sample. Interestingly, with the same Ru-doping,
superconductivity is only induced with doping at the Ge site, but remains
absent down to 1.8K with doping at the Zr site or interstitial site. Both
magnetic and transport studies have revealed the bulk superconductivity nature
for Ru-doped Zr$_5$Ge$_{2.5}$Ru$_{0.5}$ sample. The high upper critical field,
enhanced electron correlation, and extremely small electron-phonon coupling,
have indicated possible unconventional superconductivity in this system, which
warrants further detailed theoretical and experimental studies.
