The 35-year-old said she had been working in her field cutting grass when the man tried to attack her. She hit back using her sickle.
She told the BBC she had no regrets. The man had reportedly been harassing and stalking her for some time.
"He tried to rape me and I hit back with the grass-cutting weapon to save my honour," she told Ramdutt Tripathi of the BBC Hindi service.
She says she went to the police station in her blood-soaked clothes after the incident, but denied newspaper reports that she carried the head with her.
Ram Bharose, police chief of Lakhimpur Khiri district some 125 miles (200km) south of the state capital Lucknow, said they were investigating the incident.
He said the woman had a legal right to defend herself against rape and sexual attacks.
Damn straight she had a legal right to defend herself and cut that guy's head right off with her sickle.