In an open letter on its website, the company said that the incident occurred between November 2008 and May 2009 at its branches in the US and Canada.
It is not known how many hotels were targeted during the security breach, but the firm stated that the number that may have been affected is "limited".
Data such as names, card numbers and expiration dates was taken during the hack attacks and Radisson has urged guests who stayed at its hotels during the time period to check their bank statements for any suspicious transactions.
"To the extent there is any suspected unauthorized card activity, it should be reported to the bank that issued your credit card, as well as proper law enforcement authorities," the company advised.
Last month, Network Solutions revealed that details relating to 573,000 debit and credit card accounts were stolen earlier this year during a hack on its web servers.
Written by Claire Archer