Environmental group "Ecology Center" tested more than 150 car seats.
Researchers discovered 60-percent of the seats were made with chemicals such as chlorine and lead, which are sometimes used as additives in plastics.
The group did not say the levels discovered were high enough to be harmful.
But, it says there has been a 64-percent improvement between the 2008 and 2011 models.
For more information, read the report at Ecocenter.org.