Murphy, an English Springer Spaniel, has been specially trained to hunt out the mobile phone handsets - which have a particular scent.
Mobiles are a big security risk in prisons. They have been used to plot escapes, threaten court witnesses and organise crime on the outside.
About 500 have been found in jails in East Anglia in the past year.
About 60 mobile phones have been found in searches inside Norwich Prison during the past 12 months, with prisoners prepared to pay £500 to get hold of one.
Mel Barker, the dog trainer at Norwich Prison, said: "Every mobile phone has a scent which is unique to mobile phones. So we've homed in on that."
The dog, which is 15 months old, came from an animal home in Ipswich, Suffolk.