| Ioannis Demertzis Γιάννης Δεμερτζης | |
| Height Ft: | 6 |
| Height In: | 5 |
| Weight Lbs: | 200 |
| League: | Greek A2 League |
| Nationality: | Greek |
| Birth Date: | 20 July 1983 |
| Birth Place: | Panorama, Greece |
| Career Start: | 2005 |
| Years1: | 2005–2006 |
| Years2: | 2006–2007 |
| Years3: | 2007–2010 |
| Years4: | 2010–2011 |
| Team4: | Iraklis |
| Years5: | 2011–2012 |
| Years6: | 2012–2013 |
| Team6: | Keravnos |
| Years7: | 2013 |
| Team7: | Ikaros Kalitheas |
| Years8: | 2013–2014 |
| Team8: | Keravnos |
| Years9: | 2014–2015 |
| Team9: | Ethnikos Piraeus |
| Years10: | 2015–2016 |
| Years11: | 2016–2017 |
| Years12: | 2017–2018 |
| Team12: | Ermis Agias |
| Years13: | 2018–2019 |
| Team13: | Charilaos Trikoupis |
Ioannis Demertzis (alternate spellings: Giannis, Yiannis) (Greek: Γιάννης Δεμερτζης; born July 20, 1983) is a Greek professional basketball player. He is 1.96 m (6 ft 5 in) tall.[1]
After playing youth basketball with Mantoulidis, Demertzis started his pro playing career in 2005, in the Greek 2nd Division, playing with ICBS. In 2006, he moved to Iraklis, where he stayed only for one year. In 2007, he moved to PAOK Thessaloniki, where he stayed until 2010. He has also played with Marousi, Keravnos, Ikaros Kallitheas, Ethnikos Piraeus and Kavala.
He then moved to Holargos,[2] but left the team without making any appearances in order to join the newly-promoted Doxa Lefkadas of the Greek Basket League.
In 2018, he joined Apollon Patras.[3] In 2019-2020 he moved to Harilaos Trikoupis B.C.,making a good season.In 2020-2021 season he moved to Keravnos (Aghios Pavlos-Thessaloniki) B.C. Due to the COVID-19 pandemic, the league never started. In July 2021, he signed for Navarchos Votsis (Thessaloniki) B.C.