Masi Marjamäki (born January 16, 1985) is a Finnish professional ice hockey player who most recently played for Cardiff Devils in the UK EIHL.

He played his junior hockey first in his hometown Porin Ässät before moving over the ocean to the Red Deer Rebels and the Moose Jaw Warriors of the WHL before becoming professional in the 2005–2006 season.

After totaling 31 points (9 goals and 22 assists) along with 77 penalty minutes in 75 games for Bridgeport (the Islanders' top affiliate) in the 2005–06 season, Marjamäki was called up by the big club and made his NHL debut on April 18, 2006, against the Philadelphia Flyers, logging 5 minutes and 17 seconds of glory.

After a frustrating start to the 2007–08 AHL season in which Marjamäki was scratched every game, he asked the Islanders to be reassigned to Finland.

On October 4, 2018, Marjamäki having left Sweden as a free agent continued his career in the Czech Republic, agreeing to a one-year contract with Piráti Chomutov of the ELH for the 2018–19 season.