Athanasios Mastrovasilis (Greek: Αθανάσιος Μαστροβασίλης; born 18 April 1979) is a Greek chess Grandmaster (2005), three-time Greek Chess Championship winner (2015, 2018, 2021).

In the years 1993–1999 Athanasios Mastrovasilis represented Greece at the World Youth Chess Championship (three times) and European Youth Chess Championship (also three times), achieving his best result in 1995 in Guarapuava, where he took 5th place in the World Youth Chess Championship in U16 age group.

In the second half of 2010s Athanasios Mastrovasilis was one of the top Greek chess players. He competed many times in the individual finals of the Greek Chess Championship, winning the title of national champion three times (in 2015, 2018, and 2021).

In 2004 he won Acropolis International chess tournament.

Athanasios Mastrovasilis played for Greece in the Chess Olympiads:

Athanasios Mastrovasilis played for Greece and Greece 2 in the European Team Chess Championships:

Athanasios Mastrovasilis played for Greece in the World Team Chess Championship:

In 2000, Athanasios Mastrovasilis was awarded the FIDE International Master (IM) title and received the FIDE Grandmaster (GM) title five years later. He achieved the highest rating in his career on September 1, 2010, with a score of 2556 points, he was then 6th among Greek chess players.