Kaja Eržen (born 21 August 1994) is a Slovenian professional footballer who plays as a right back for Serie A club Fiorentina and the Slovenia women's national team.

After a run of games where Eržen scored 27 goals in 19 starts, she decided to move abroad to Austrian club Carinthians in 2014.

The team clinched seventh position in the league and saved themselves from relegation, before Eržen chose to return to her native Slovenia and sign with Olimpia Ljubljana for the 2016–17 season.

During her two seasons with Tavagnacco, Eržen played mostly as a winger and helped her side compete near the top of the Serie A table as well as reaching the Coppa Italia semi-final.

She now plays that position for both club and country, and made an appearance in the 2021 Coppa Italia final for Roma.