Police were called to a report of a serious sexual assault near Preston bus station at around 3.30am on Sunday, February 27.
A woman in her 20s reported she had been attacked by a man in a grassed area off Crooked Lane.
A 24-year-old man from Preston was later arrested on suspicion of rape.
He remained in custody for questioning on Monday afternoon (February 28).
"An investigation is underway and enquiries ongoing," a spokesman for Lancashire Police said.
"The woman is receiving support from trained officers."
Anyone with information can contact the police by calling 101, quoting log number 0255 of February 27.
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