The Midlands city recently scored 20 out of 20 for the green-space indicator in the Forum for the Future Sustainable Cities Index 2010, which tracks progress on sustainability in Britain's 20 largest cities.
The charity Forum for the Future checks on the environmental performance and quality of life in UK cities in an effort to reward their achievements, encourage healthy competition, and provide local citizens with the tools to hold their leaders to account.
It is the second year in a row that the city had come top, thanks to 22 gongs across the city in 2010.
Leisure chief councillor David Trimble said: "Nottingham boosts many green spaces and our officers work hard to keep these areas safe, clean and green."
Eddie Curry, Nottingham council head of parks and open spaces, added: "We focus on building strong partnerships within the council to source external funding for improvements to our parks."
The service recently secured money for wide-ranging improvements across the city, including work to 40 new playgrounds and several new outdoor multi-use games areas.
Almost £2m in Section 106 money will be spent over the next year, while more than £250,000 of area capital money will be used to finance a new skate park in the city next March.
Curry said his team were also about to put in a £5m lottery bid for improvements to a city forest. The proposed changes are set to include tree planting, building new visitor paths and renovating two buildings.
In another record year for the city, 13 parks won Green Flags and nine community green spaces gained Green Pennants. RHS Your Neighbourhood awards went to 130 community groups.