Martin Ostertag (born in 1943) is a German classical cellist and music educator.
Born in Lörrach, Ostertag studied cello with Leo Koscielny at the Hochschule für Musik Karlsruhe and with André Navarra in Paris.
In 1967 he was a prizewinner of the international competition in Vienna, and in 1968/69 he won the national selection of the Deutscher Musikrat Konzert junger Künstler.
He undertook numerous concert tours and gab master classes in Argentina, Brazil, Canada, Germany, Finland, Italy and Japan.
Together with Nicolas Chumachenco, Erika Geldsetzer and Benjamin Rivinius, Ostertag founded the Villa Musica String Quartet, with whom he won two ECHO Klassik prizes for recordings of Mozart's String quartets.