The green group, WWF, is calling on people around the world to switch off their lights this Saturday at 8.30pm for one hour to show their commitment to making the Earth a better place.
It is the third year that Hong Kong will be involved in Earth Hour, which was launched in Australia in 2007.
More than a billion people from 125 countries and cities - including 2.5 million Hongkongers - took part in last year's campaign.
Around 2,500 companies and buildings, 230 schools and youth groups, and all universities in the city switched off their lights last year for a brighter future. Almost all the lights of buildings along Victoria Harbour were turned off. The Symphony of Lights was also cancelled that night.
The theme of this year's campaign is 'Go Beyond the Hour'. WWF hopes Earth Hour will not be just about switching off the lights for 60 minutes. Even after the campaign, the organisation urged people to think about what they can do to protect our environment. Last year's theme was climate change.
Lee King-yin, WWF Hong Kong's communications manager, said the theme this year is broader because climate change is not the only threat the earth is facing.
Apart from saving electricity consumption for one hour, Lee said they wanted people to lead by example.