Posti will use the remote-controlled aircraft to deliver packages to Suomenlinna, a former island fortress that forms part of Helsinki.
The drones are expected to take to the air in early September, initially make deliveries to Suomenlinna residents for orders made in the online store Verkkokauppa.com.
Posti said it had informed island residents of the week-long trial.
"As far as we know we are the first in Europe to attempt delivery of packages in an urban environment using helicopter drones," said Posti communications chief Anne Huhtala.
Other mail, such as letters and periodicals, will be delivered by ferry as usual.
The Posti experiment was first reported by the daily Helsingin Sanomat.