Maroussi B.C. (Greek: K.A.E. Μαρούσι) alternately translated as Marousi, Amaroussio, or Amaroussion, is a professional basketball club that is based in Maroussi, a northern suburb of Athens, Greece. The club's full name is Gymnastikos Syllogos Maroussi Basketball Club, which is commonly abbreviated as G.S. Maroussi B.C.. The club currently competes in the top-tier Greek Basketball League (GBL).

The multi-sports club Gymnastikos Syllogos Amarousiou (Amarousi Sports Club) was founded in 1896, the same year that Maroussi native Spyridon Louis won the Olympic marathon at the 1896 Summer Olympics. The club's men's basketball section started in 1950.

The basketball section played in the Greek minor leagues for the first two decades of its existence. It reached the Greek top division, the A National Category (Alpha League) in 1969, where it played for one season before being relegated.

In the 1970s, the club was led by Nikos Darivas at point guard and Dimitris Fosses at center, and starting with the 1971–72 season, the club played in the Greek top division for all but one year of the following decade. Maroussi qualified for the European third-tier level FIBA Korać Cup's 1978–79 season.

The club was then relegated after the 1980–81 season, and alternated between the second-tier level A2 League and the third-tier level B League for the next 18 years.

Maroussi was promoted back up to the Greek First Division for the 1998–99 season, and moved from the Spiros Louis Gym to the newly constructed Maroussi Saint Thomas Indoor Hall.

Maroussi won the title of the European second-tier level FIBA Saporta Cup, during the 2000–01 season. That team was coached by Vangelis Alexandris, and it featured the inside-outside scoring tandem of Jimmy Oliver and Ashraf Amaya, as well as the rebounding skills of Vassil Evtimov. Maroussi became the sixth Greek team to win a European continental-wide title.

The club at this time received financial backing from Greek businessman Aris Vovos.