The woman found the handbag at around 10am on Thursday in the Zona Universitària station in Barcelona.
She handed the bag in to a metro worker at the station who reported it to the metro's central control centre.
The bag was found to contain €8,575 ($9,673) in cash according to Barcelona Metropolitan Transport (TMB), which runs the public transport system.
Barcelona Metro tweeted the news on Thursday.
Shortly after, a woman reported the bag missing at Terminal 1 Barcelona's El Prat airport and was reunited with her lost handbag shortly after.
TMB did not record the identity of the woman who found the handbag and is now looking for her so they can put her in touch with the bag's owner, who wants to thank her.
It is not the first time someone has left a large amount of money on public transport in Spain. Only two weeks ago, a wallet containing €7,600 that was found in the Arc de Triomf station in Barcelona.