The body of Nadia Jones was found in her flat in Tremorfa on Friday.
Five men, two aged 36,  the others aged 27, 30 and 32, were held overnight at Cardiff Bay police station.
Specially trained officers are supporting Ms Jones's family, while an incident room has been set up as police appeal for information.
Detectives are also awaiting the results of a post mortem examination.
House-to-house inquiries were also being carried out in Meirion Place, off Mercia Road, where Ms Jones lived.
Det Supt Chris Parsons of South Wales Police said: "We are doing all that we can to establish what happened to Nadia in the moments leading up to her death."
The officer said it was vital anyone with information about her death came forward, especially anyone in the area between 20:00 BST on Thursday evening through to about 13:00 on Friday.
Police are continuing to question five men arrested in a murder investigation after the body of a 38-year-old woman was found in a Cardiff flat.