Ponsonby is one of the city's most sought-after post codes. There were 14 residential sales in Ponsonby in April, with a median selling price of $1,469,500, according to latest Real Estate Institute figures.
Bayleys agent Peter Sullivan said the land was zoned for school use and would need to be rezoned through a resource consent process to allow building to take place. It had been used as an access way for the school in the past and was "excess to requirements".
Though there was plenty of interest in the land already, the vendors were yet to receive an offer and it was difficult to estimate what it might be worth.
Mr Sullivan said the buyer could potentially build two large homes on the site, which would probably be subject to standard design and character rules for the area. He did not know whether more intensive infill housing was possible on the site.
"The Marist Brothers have decided to sell. They're considering their options. We haven't received an offer and I don't know what it's worth.
"We're asking the interested parties to go away, do their due diligence and come back with some suggested offers."
St Paul's chairman of the board, Denis Wood, said the land up for sale was surplus to what they needed at the school.
"We have around 6 hectares of land - more than enough land to accommodate a growing school."
Mr Wood said the Marist Brothers Trust had agreed that all proceeds from the sale of the land would go back into the school, to help with a new redevelopment project.
The project involves new classrooms, an administration block and a new middle school being built by February 2017.
St Paul's College is an integrated Catholic boys' college founded by the Marist Brothers.
The school's website says Marist education is based on a holistic vision "that consciously seeks to communicate gospel values".
The school charged "attendance dues" last year of $396 for Year 7-8 students and $772 for Year 9-13 students. The Marist website says the money was used to repay loans for building work, insurance costs and other property-related expenses.