It happened in the University Street area of south Belfast in the early hours of this morning, Tuesday, March 7.
Detective Inspector Zoe McKee of the RCU said: “A woman aged in her 20’s reported that she was assaulted by a man in the doorway of commercial premises in the area at around 12.40 am.
“A 25 year old man has been arrested on suspicion of rape and is currently in custody assisting officers with their enquiries.”
DI McKee added: “ I am appealing for anyone who was in the area of University Street around the time this incident took place and who noticed any suspicious activity to contact detectives at Ladas Drive on 101 quoting reference number 19 07/03/17.
“Information can also be given anonymously through the independent charity Crimestoppers on 0800 555 111.”