Illawarra Coke Company has been fined $1500 after two complaints from a nearby primary school about a "rotten egg" smell from the 100-year-old Corrimal cokeworks.
The NSW Environment Protection Authority investigated complaints from the Corrimal East Public School in late June about bad smells that affected the school for a short time.
Chief environmental regulator Mark Gifford said the EPA notified NSW Health as a precaution and was told that no-one required any medical attention.
Illawarra Coke Company was fined because its licence did not allow the emission of offensive odours past the site boundary.
"The company has revised its procedures relating to restoring ovens following maintenance activities, which will minimise the likelihood of a recurrence of the incident," Mr Gifford said.
"The EPA has observed a significant improvement in the environmental performance of ICC over the last 10 years, to the point where odour incidents are rare and there has been a progressive reduction in the number of odour and other complaints received."
ICC managing director Rex Wright said the odour complaint was the first in two years.
"We were extremely disappointed that this happened and the changes will greatly minimise the likelihood of this particular issue ever happening again," he said.
"We have devoted a significant amount of resources into reducing our impact on the surrounding community since taking ownership in 1996."