The fire was completely put out "at 9:00 am on Saturday," the emergencies ministry said in a statement.
The levels of radiation were slightly elevated at the Chernobyl site, which is about 100 kilometres from the Ukrainian capital Kiev, it said.
The blaze came within about 20 kilometres of Chernobyl after breaking out Tuesday afternoon, but officials said it posed no danger to the plant and firefighters brought it under control within a day.
Officials gave few details of the possible cause of the fire but Interior Minister Arsen Avakov said authorities had not ruled out arson.
The fire struck just two days after Ukrainians marked 29 years since the Chernobyl nuclear disaster.