Ghulam Hussain Gopang, the brother of the woman, was arrested following the incident in the Loung Gopang village near Kot Diji of Khairpur district, they said.
Gopang confessed to have murdered his sister, saying he was motivated to commit the crime on the suspicion that his sister was in an illicit relationship with a local man, police said.
The woman's husband, however, did not comment on his wife's murder, the Dawn reported.
Every year, hundreds of women are killed in Pakistan by their male relatives for "dishonouring" the family.