Swindon Police are appealing for witnesses following an assault in the town centre yesterday - 9 June.
A spokesperson said: "We responded at approximately 4.45pm to the incident at the junction of Regent Street and Canal Walk, where it was reported that a woman had been assaulted.
"The victim, a woman in her 20s, suffered significant injuries to her head and was taken to Great Western Hospital, where she remains.
"A woman in her 40s, who was also taken to Great Western Hospital for injuries to her head, has been arrested on suspicion of GBH with intent and remains in hospital.
"A scene was put in place while we carried out our enquiries and was cleared shortly after 9.30pm."
Witnesses are asked to call 101 and quote crime reference number 54210055193.