Napier was the top-scoring Scottish university in the People & Planet Green League 2012 and 26th overall — out of 145 universities — in the UK league.
It eased ahead of Edinburgh University thanks to strong scores for its environmental and carbon management policies, as well as good engagement with students and staff on environmental issues.
Meanwhile, Queen Margaret University came second in Scotland and 38th nationally.
Professor Dame Joan Stringer, principal and vice chancellor of Napier, said: “We are working very hard to reduce our environmental footprint, and so to again be recognised with a First Class award by People & Planet is extremely pleasing.
“The award builds on our recent success in gaining the Carbon Masters Standard.”