Police on Tuesday said Wichai Wettana, 40, admitted he attacked the antelope with a steel pipe after he saw the animal wandering in the factory on the evening of Dec 19.
Mr Wichai said he beat the animal to the ground with a steel pipe because he was afraid it would be harmed if it got in the way of factory machinery.
After the serow was beaten unconscious he and six colleagues carried it to a pickup truck. The animal was taken into a nearby forest and released, he said.
When officials checked the area where he said the serow was released, they found its hoof prints, but did not see the animal.
The incident was captured on video, which was then posted on the internet.
Internet users who saw the video clip of Mr Wichai attacking the serow accused him of being cruel to a "harmless" animal.
The cement works in Sara Buri is near Khao Yai National Park.