Louise Mai Jansen (born April 14, 1984) is a Danish former swimmer, who specialized in freestyle and individual medley events.

She is also an eighth-place finalist in the 200 m individual medley at the 2010 European Aquatics Championships in Budapest, Hungary with a time of 2:17.37, just eight seconds off the record set by Julie Hjorth-Hansen in 2009.

She cleared a FINA B-standard entry time of 2:02.20 (200 m freestyle) from the Danish Open in Copenhagen.

[7] In the 200 m freestyle, Jansen raced to fourth place and thirty-fourth overall on the same heat as Athens by exactly one second ahead of Singapore's Lynette Lim in 2:01.30.

[9] At the 2009 FINA World Championships in Rome, Italy, Jansen helped her Danish team (Hjorth-Hansen, Ostergaard, and Friis) to dip under an eight-minute barrier and broke a new record of 7:55.56 in the 4 × 200 m freestyle relay, but finished only in twelfth place overall from the preliminary heats.