The facility, which was opened last Sunday to a crowd of about 500 people, is the first of its kind at the school.
Principal Simon Midson said students were excited about having more sporting options.
“The students have always been able to play basketball and netball because we had the courts,” Mr Midson said.
“Now they will be able to play badminton, volleyball and indoor soccer.”
Premier Colin Barnett and Senator Linda Reynolds opened the George and Despina Berbatis Gymnasium.
Guests Perth MLA Eleni Evangel, who was the first teacher appointed at the school, and 1992 Olympic gold medallist Paraskevi Patoulidou attended the opening ceremony.
Mr Midson thanked the Australian and WA governments, the Hellenic Community of WA and the Berbatis family for co-funding the gymnasium.
“This state of the art gymnasium is a gift to current and future generations of St Andrew’s Grammar students,” he said.
“The gymnasium will stimulate their interest in sport and encourage them to embrace the mantra of a healthy mind in a healthy body.”
The gymnasium complex can host indoor activities including basketball, netball, volleyball, badminton and includes a multi-purpose classroom for dance and physical education programs, along with showers and change room facilities.