Sangeeta Kashyap was recruited as a biology teacher in the central state of Madhya Pradesh in 1990.
School authorities say they do not know when she was last paid a salary, but she is still listed as an employee.
State education officials told the BBC the teacher would be removed from her post. She is thought to have set an Indian record for staff absenteeism.
Ms Kashyap spent her first year teaching in a school in the town of Dewas, after which she took three years of leave.
In 1994, she was transferred to a school in the city of Indore but then applied for maternity leave and has never turned up for work.
Letters sent by the school to her address have remained unanswered, Sushma Vaishya, principal of the Government Ahilya Ashram School in Indore, said.
An education department official said they had written to education authorities in the state capital, Bhopal, to have Ms Kashyap removed from her post.
"I have no idea why nothing was done. We are writing to them again to remove her," Sanjay Goel told BBC Hindi's Shuraih Niyaazi.
The school is allowed to have three biology teachers, but only two are filled - with the third held by the absentee teacher.
Correspondents say absenteeism is a pervasive problem in government-run schools in India.
A World Bank study in 2004 found that 25% of teachers were absent from school, and only about half were present during unannounced visits to government primary schools.
Ms Kashyap's whereabouts remain unknown and she has not commented on the reports about her in the Indian press.
It is also not clear why she did not return to work or if she has been working elsewhere - correspondents say the fact her post remained empty for so long says little for the competence of education officials.
An Indian state school says one of its teachers has been absent for 23 years of her 24-year career.