The punishment was carried out in a remote village in Muslim-majority Bangladesh on the orders of village elders, local police chief Enamul Monowar told AFP by telephone.
The village elders found Kamala Begum, 38, a mother of four, guilty under Islamic sharia law of chatting with an unidentified Hindu man, Monowar said. Hindus make up around 10 percent of Bangladesh's population.
"The villagers got bundles of 25 sticks and hit her four times on the back. They claimed it was a symbolic punishment. But she's humiliated and has been in great mental pain," Monowar said.
It was the third such reported case in two weeks in the country and stirred concern among women's groups in Muslim-majority but officially secular Bangladesh, about what they say is a rise in the brutal treatment of women under locally applied Islamic laws.
"In the last few months, we have seen villagers invoking sharia to mete out barbaric punishments to women," said Salma Ali, the head of rights group Bangladesh National Woman Lawyers Association.
Police have arrested one man and are looking for others who meted out the punishment to the woman in Shason in northeastern Bangladesh, Monowar said.
Earlier this month a man and a woman were caned for adultery after being convicted by a village court, police said.
Village courts are common in Bangladesh, particularly in more conservative rural areas, but are not recognised as legitimate courts of law.
Also this month, a 22-year-old unwed woman was caned 39 times and left fighting for her life after saying a neighbour was the father of her six-year-old son.
The case caused a national outcry with Premier Sheikh Hasina ordering the woman shifted from her village home to the capital for treatment. The woman is now in a stable condition.
So far, Bangladesh has been little affected by the spread of hardline Islamic sentiment that has badly shaken its South Asian neighbour Pakistan.
But women's rights groups say there has been a spike in the number of "fatwas" -- judgments in line with sharia law -- in rural areas.
"In the last few months, we've seen villagers invoking sharia to mete out barbaric punishments to women," said lawyer Ali.
"It's disturbing sign and a real concern. It shows some parts of the country are becoming more conservative," she said.
Bangladesh has been ruled by female leaders for 16 of the last 19 years and prides itself for empowering women.
But although women hold high government and private sector posts, a move last year to give equal property rights to women was scuttled by Islamist protests.
The Awami League government has vowed to eradicate militancy from the country, hit by series of blasts by outlawed Islamic groups in 2005, and has warned of "zero tolerance" for harsh sharia punishments.