A man walked into the Premier Express store in Mansfield Road, Alfreton, shortly after 7am on Saturday, February 28.
He threatened a member of staff with a knife and made off with a small amount of cash, running off along Prospect Street.
Detectives believe the same man went into the Stop and Shop store in Market Street, South Normanton, at about 5.45pm that day.
The offender threatened a member of staff with a knife and demanded cash but was challenged and fled empty-handed.
Nobody was injured in either of the offences.
CCTV stills have now been issued of a man police want to speak to in connection with both incidents.
If you recognise the man in the CCTV stills, call police on 101 or Crimestoppers on 0800 555 111.