More than a thousand pupils were ordered from the building during the incident at Stonelaw High School, in Rutherglen.
Emergency services, including fire crews and a hazardous response team, raced to the scene, in Calderwood Road, yesterday afternoon.
Firefighters, wearing breathing apparatus and chemical suits, immediately sealed off the building until it was declared safe.
The alarm was raised at around 2.20pm yesterday. It is not yet clear what the chemical involved in the spill was.
Strathclyde Fire and Rescue said the staff member was taken to Hairmyres Hospital as a "precautionary measure".
A spokesman said: "At 2.20pm on Tuesday afternoon, Strathclyde Fire and Rescue mobilised crews to Stonelaw High School in Rutherglen following reports of a small chemical spill.
"Following initial checks by our firefighters, our specialist hazmat response team was summoned and our scientific advisors carried out atmospheric monitoring. It is understood that exposure to the spill was very limited.
"We can confirmed that there is no danger of any further contamination.
"Our staff will remain on site until the monitoring operation concludes and we are sure that no residue remains."
A spokeswoman for South Lanarkshire Council confirmed that the school would open as normal today.
She said: "There was a chemical spill in the science department on Tuesday afternoon.
"No-one was injured and guidance was taken from the fire service.
"The school was evacuated as a precaution."