The Crown agency has sent a letter to members warning them to ``take appropriate steps" to secure personal and credit-card information.
The province's privacy commissioner is investigating the theft on Sept. 18.
Commission spokesman Bob Spence said there were two groups of stolen data — one with just names and addresses, and another that included credit-card numbers.
Spence couldn't say how many people were affected.
He says the science centre reported the theft to the privacy commissioner as required.
The Ontario Science Centre said only people who received letters with a four- or five-digit number at the bottom had their credit card numbers compromised.
"We deeply regret this situation and would like to assure you that we are taking immediate steps to review our security procedures," Catherine Paisley, the centre's director of education, wrote in the letter.
"I would like to express my sincerest apologies for this breach of privacy."