Although the bookshop will remain in the building, the association is considering "development options" to make the best use of the site.
OUSA chief executive Debbie Downs said the association owned 100% of UBS, and UBS owned the building, which was much larger than the shop.
The OUSA executive voted to buy the building, and took control of it, in December.
"The change is that OUSA is going to take control of the building directly," Ms Downs said.
"OUSA will continue looking at development options of the building but this is still at the very early stages, and the ownership change has not yet happened."
There were "many possibilities" for the wider building, which included about 500sqm upstairs, and an underutilised space on the ground floor of about 150sqm.
"This is all part of the exciting development plan.
"OUSA has the capacity to investigate these whilst enabling the bookshop to focus on what it does so well - being Dunedin's finest bookshop with knowledgeable staff, excellent service, a comfortable shopping environment and a fabulous selection of books and stationery."
Ms Downs declined to say how much OUSA had paid for the building.
The association also announced last year it had bought Starter's Bar, but likewise did not reveal how much it paid.
The bar is due to be refurbished in February, before it reopens.