The website Cozycot initially had a target of just 1,000, but has now far exceeded its expectations, The Straits Times reported.
The bras will benefit young women in orphanages and slums in Bali and Cambodia.
Cozycot founder Nicole Yee had expected to collect 1,000 bras by the end of its three-week campaign, but said she was surprised by the response.
"The overwhelming response from women is really heartening. It shows that women in Singapore will not think twice to band together for a good cause," Yee said.
Out of the 10,000 donated bras, over 400 were new - some complete with price tags.
Encouraged by the success of this effort, Yee said she hoped Cozycot's 150,000 members to do more for others.
"Being a woman's website, it is only natural that Cozycot helps other women. We will organise programmes which will provide an avenue for women to do something meaningful for others," she said.