The U.S. Federal Trade Commission terminated the waiting period for the acquisition under the Hart-Scott-Rodino Antitrust Improvements Act, Nordion said in a statement.
The company said in June it had received a request for additional information from the U.S. regulator.
Nordion also said on Friday that it received a no-action letter from the Canadian Competition Bureau.
The deal is expected to close in the second half of this year.
Nordion is a leading producer of molybdenum-99, an isotope used in medical imaging, while Sterigenics is a sterilization services provider owned by private equity firm GTCR LLC.
Nordion's U.S.-listed shares were up 3 percent at $12.80 in premarket trading.
(Reporting by Ashutosh Pandey in Bangalore; Editing by Kirti Pandey)