The 'Titanic' star beat off competition from Bono, Brad Pitt and actor Ed Begley Jr to top the male category in the survey to find the most popular eco-friendly stars, reports Contactmusic.
The poll was carried out by GreenDaily.com and Bebo.com.
Talk show host Winfrey out-shined Angelina Jolie, Hayden Panettiere, Gwyneth Paltrow and Sir Paul McCartney's ex-wife Heather Mills to lead the female category.
Meanwhile, singer Mariah Carey has been named the least environmentally friendly star, following reports she regularly flies her personal trainer from the Caribbean to New York to keep her fit.
John Travolta joined her on the hit list, after it was found the qualified pilot generates 800 tons of carbon emissions each year flying around the world.