Agios Konstantinos, Phthiotis
{{Infobox Greek Dimos
|name = Agios Konstantinos
|name_local = Άγιος Κωνσταντίνος
|type = municipal unit
|image_map = DE Agiou Konstandinou Fthiotidas.svg
|map_caption = Location within the regional unit
| periph = Central Greece
| periphunit = Phthiotis
|municipality = Kamena Vourla
|pop_municunit = 2952
|pop_community = 2786
|population_as_of = 2021
|area_municunit = 72.29
|elevation =
|coordinates = {{coord|38|45|N|22|52|E|format=dms|display=inline,title}}
|postal_code =
|area_code =
|licence = ΜΙ
|website =
|image_skyline =
|caption_skyline =
}}
Agios Konstantinos ({{langx|el|Άγιος Κωνσταντίνος}}) is a town and former municipality in Phthiotida (Phthiotis), Greece. After the 2011 administrative division reforms it became part of the municipality of Kamena Vourla and it is now ranked as a municipal unit,{{Cite web|url=http://www.et.gr/idocs-nph/search/pdfViewerForm.html?args=5C7QrtC22wGYK2xFpSwMnXdtvSoClrL81-32jgAMSfbnMRVjyfnPUeJInJ48_97uHrMts-zFzeyCiBSQOpYnT00MHhcXFRTsb2fGphpq4MKX2ZkaHobySNnvZCNHXvYVvlf80XevW0Q.|title=ΦΕΚ B 1292/2010, Kallikratis reform municipalities|language=el|publisher=Government Gazette}} with an area of 72.292 km2.{{cite web|url=http://dlib.statistics.gr/Book/GRESYE_02_0101_00098%20.pdf |publisher=National Statistical Service of Greece |title=Population & housing census 2001 (incl. area and average elevation) |language=el |url-status=live|archiveurl=https://web.archive.org/web/20150921212047/http://dlib.statistics.gr/Book/GRESYE_02_0101_00098%20.pdf |archivedate=2015-09-21 }} Its population was 2,952 in 2021.
The town has a harbor with a regular ferry-boat connection to the islands of Skiathos, Skopelos and Alonnisos.{{cite web|url=http://www.ferrylines.com/en/ferries/region-by-destination/162/ |title=Region by Destination |accessdate=2011-08-28 |url-status=dead |archiveurl=https://web.archive.org/web/20110815141455/http://www.ferrylines.com/en/ferries/region-by-destination/162/ |archivedate=2011-08-15 }} These islands are part of the Northern Sporades archipelago.