The 6.2m (20ft) bra was crocheted by the Swindon Bitch and Stitch knitting group to raise funds for the charity Against Breast Cancer.
Despite attracting about 200 views, the bra, listed as "used", did not sell.
Tracey Major, from the group, said: "It's very heavy, each cup weighs about 5kgs so it could be used as beanbags."
Measuring 6.2m wide and 2m high, the giant bra took around four months to create.
Along with bras belonging to Honor Blackman, Barbara Windsor, and Twiggy, it is currently on display at the Brunel Centre in Swindon.
Ms Major said they had been hoping to find a "good home" for it and raise "a giant amount of money".
"I listed it as used because so many people were touching it and doing selfies with it and I thought I can't sell that as new," she said.
"But if it doesn't sell, I'm not too fussed because we can donate it to the charity and they can use it and take it around to exhibitions with them."
A giant bra designed to raise awareness of breast cancer, which failed to sell on the auction website eBay is to be relisted, its makers say.