The incident took place in Shahganj locality of Jaunpur, about 250 km from the state capital Lucknow.
In a suicide note, she blamed the manager for prompting her to take the extreme step.
"The note said the school manager was sexually harassing her for a long time on false assurances to marry her," Senior Superintendent of Police SK Bhagat told reporters here.
"Preliminary investigations reveal the principal had learnt that the manager was only interested in an illicit relationship and not in marrying her," he said.
Efforts are on to arrest the manager.
"She is being treated for multiple burn injuries. Her condition is extremely serious," an official said.
Jaunpur: A school principal here set herself afire outside the home of the school manager who she claimed had been sexually harassing her, police said Thursday. The woman's condition was described as "extremly serious".
First Published: Thursday, January 27, 2011, 11:50