Residents will not be able to visit Hallowes Crescent Post Office, off Hayling Road near South Oxhey, from 5.30pm on April 25 until 1pm on May 3.
It is set to be revamped into a “new-style branch” with Post Office services offered alongside the retail counter, which allows longer opening hours.
Post Office Network Provision lead Zoe Hall said: “The safety of our customers is of paramount importance to us, and to allow this change to take place, Great Hallowes Post Office branch will need to close, temporarily.
“However, customers will soon benefit from greatly improved opening hours, which will make it much easier for Post Office customers to pop in.”
The branch currently opens from 9am to 3.30pm, Monday to Friday. After the refurb, it will open every day and the hours will be 5.30am to 8.30pm Monday to Friday, 6am to 8.30pm Saturdays, and 6am to 7.30pm on Sundays.
While it is shut, residents are advised to visit Prestwick Road Post Office in Station Approach or Eastbury Road Post Office.