The school received development approval from the City of Stirling in March this year, with work beginning last week.
St Andrew�s principal Simon Midson said the gymnasium would be completed late this year.
�The gymnasium project provides students with a first-class sporting facility,� he said.
�Also, the complex will facilitate assemblies, examinations and functions.�
The development will include a full-size basketball court, classroom and changerooms.
Mr Midson said the school had received government and private funding for the project, as well as a low-interest government loan.
The principal said the gymnasium would provide the capacity for a variety of sports to be played including basketball, netball, badminton and indoor soccer.
�The St Andrew�s Grammar community is very excited about the new gymnasium facility,� he said.
Hellenic Community of Western Australia president Gary Mitchell said he was thrilled with the development�s approval.
�I am utterly delighted with the positive growth and directions at St Andrew�s Grammar,� he said.
�Enormous thanks must go to the Berbatis Family, together with the members of the Hellenic community, who have completely embraced the school and have afforded the opportunity to progress the school�s facilities with the construction of the new sports facility.�
Project architect Jeremy Feldhusen said the multimillion-dollar development would form an important part of the school�s development.
�While primarily a sports hall, the building is a multipurpose facility, forming an integral �piece of the puzzle� to the eastern edge of the campus,� he said.