Dang Huu Dung, a professor at the Agriculture and Forestry University, received acid burns to a third of his body, the Thanh Nien newspaper website reported.
The professor told reporters that a former student used a large bowl to splash him with the acid before chasing him with a knife, the report said.
Thanh Nien report said that Police arrested Tran Xuan Thanh, 28-year-old who finished his four-year course in 2006 but did not graduate because he failed the English test on mechanics.
It said the former student allegedly told police that he recently asked Dung to help him apply for another English test but the professor refused, saying it was too late.
"I thought Mr Dung was not fulfilling his responsibilities towards his students," Thanh allegedly told police, adding that he took five litres (1.3 gallons) of acid to the school.