More than 60 students were hospitalized in the city of Tripoli after drinking contaminated tap water.
The students, all below 12 years of age, were taken to a hospital after suffering from pain in the abdomen, vomiting, diarrhoea and breathing difficulty.
The children are students of Hayy al-Nozha school, Xinhua reported citing Voice of Lebanon radio.
A doctor at the hospital, Jalal Abbous, said the kids "will be monitored for 24 hours. The water is also being tested to know the source of the contamination".
The results of medical tests will be revealed Friday, he said.
In a similar incident in May last year, several students and a teacher in a public school suffered from food poisoning after having lunch during a school trip.