The man fell through the roof of a silo Tuesday night and into the cistern, which contained the corrosive liquid, heated to about 160 to 175 degrees, at Munksjo Paper factory in Billingsfors, factory manager Ulf Maxen told The Local.
Maxen said he was unsure why the victim, who had worked at the factory more than 20 years, was on the roof, from which he is believed to have fallen about 26 feet.
"Some people in the area couldn't find him and then they heard him and were able to figure out where he was," Maxen said.
The lye is used in paper manufacturing.
The Local said emergency crews and the man's co-workers worked through the night to try to gain access to the cistern and recovered his body Wednesday morning, when the plant closed.
"There's a feeling of incredible sorrow here today," Maxen said.
The accident is being investigated by police and the Swedish Work Environment Authority.