Saran District Magistrate Abhijit Sinha said the eight children died after the mid-day meal at Dharamsati primary school in Masrakh in Saran, about 100 km from here.
More than 60 children fell ill and were admitted to hospital for treatment, he added.
Angry over the deaths, hundreds of people took to the streets in protest and surrounded the local police station demanding action against school teachers and officials responsible.
Bihar Chief Minister Nitish Kumar has expressed shock over the incident and announced a compensation of Rs 2 lakh to the kin of each of the dead school children. He also summoned Education Minister PK Sahi to discuss the issue. He called an emergency meeting later in the day.
In Bihar, widespread corruption is reported in the mid-day meal scheme and government guidelines on food quality are ignored.
In past, dead lizards, frogs, insects and a rat were found in the food cooked for the mid-day meal, angering students and parents.