Part of Tabard Gardens was cordoned off on Thursday morning while police investigated reports of a 'serious sexual assault' in the park.
The incident is said to have occurred in the play area at about 8pm on Wednesday evening.
'Police are investigating an allegation of rape from a female that occurred in Tabard Gardens, SE1 on Wednesday, 7 November," said a Scotland Yard spokeswoman.
"Officers from the Child Abuse and Sexual Offences Command investigate."
Anyone with information is asked to call 101.