The two armed robbers threatened terrified staff in Nando's at Castlegate Way just before noon on Friday.
The pair made off with cash from the till, said police, who are now appealing for witnesses to the robbery.
Noone was hurt in the incident, they said.
A West Midlands Police spokesman said: "Police were called to an armed robbery at Nando's, Castlegate Way, Dudley, just before 11.45am on Friday.
"Two masked men holding a knife and hammer threatened staff and made off with cash. Noone was injured."
Anyone with information is asked to contact police, quoting log number 824 of 15/11/19.