Professor Maathai is also vocal on women's rights
Professor Maathai, also Kenya's deputy environment minister, is the first African woman and environmentalist to win the prestigious award.
The 64-year-old was honoured for her campaign to save Africa's trees and for promoting social, economic and cultural reforms that are ecologically viable.
She was described as an example for all Africans seeking democracy and peace.
Green belt
"There can be no peace without equitable development and there can be no development without sustainable management of the environment in a democratic and peaceful space.
"This shift is an idea whose time has come," said Prof Maathai in her acceptance speech.
HAVE YOUR SAY It is another example which shows that women can create a positive impact beyond their communities
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Introducing her at the prize-giving ceremony, Nobel committee chairman Ole Mjoes said that conflicts such as in the Middle East and Sudan's Darfur region had their roots in competition for natural resources.
"Environmental protection has become yet another path to peace... There are connections between peace on the one hand and an environment on the other in which scarce resources such as oil, water, minerals and timber are quarrelled over," he said.
Prof Maathai is the founder of the Green Belt Movement, which has planted 20-30 million trees in Africa to counter forest loss and slow the spread of the deserts.
The movement went on to campaign on education, nutrition and other issues important to women.
Trees can galvanise people, Maathai says
Prof Maathai beat a record 194 nominations, including former chief United Nations weapons inspector Hans Blix and the head of the UN energy watchdog, Mohamed ElBaradei, to win the prize.
She picked up a cheque for 10 million Swedish Kronor ($1.4m), a gold medal and a diploma at the prize-giving ceremony in Oslo's city hall.
The event is being held on the anniversary of the death of Swedish philanthropist Alfred Nobel, who launched the peace prize in 1901.
— The 2004 Nobel Peace Prize was awarded today to  from Kenya. She is the first African woman to win the Peace prize, and the 12th woman to win the prize since its inception in 1901. The Nobel committee cited "her contribution to sustainable development, democracy and peace" as the reasons for awarding the prize. It is the first Peace prize awarded to an environmentalist.

Dr Maathai is a member of parliament in Kenya, the country's deputy environmental minister, and holds a  in  from the University of Nairobi. For seven years she was the director of the  in Kenya, and is most known for founding the  — a non-governmental organization dedicated to environmental conservation and protecting forests. Since its founding in 1997, the organization claims to have planted over 30 million trees, in the process employing thousands of women — offering them empowerment, education and even family planning.

The GBM organises rural women in Kenya to participate in environmentally friendly activities such as reforestation; economically-conducive activities like eco-tourism and training in forestry and food processing; as well as community development. 

On her Green Belt Movement project, Dr Maathai told the  Courier in 1999, "If you want to save the environment, you should protect the people first, because human beings are part of biological diversity. And if we can't protect our own species, what's the point of protecting tree species?"

In accepting the prize, Dr Maathai said that she was humbled by the recognition and uplifted by the honor of receiving the award, and discussed social and environmental problems that still challenge Africa and the rest of the world. The award includes a cash component of 10 million Swedish Kronor (approximately US$1.4 million). 

Dr Maathai's project was opposed by the Kenyan government during 's  rule, and Dr Maathai's demonstrations to protect the forests often met with violent resistance; eventually, she was jailed.  

"The government thinks that by threatening me and bashing me they can silence me," Dr Maathai said. "But I have an elephant's skin and somebody must raise their voice."

In 1997 Dr Maathai ran for president on the Liberal Party of Kenya ticket. In 2002 — after Moi's  party lost the presidential race — she was elected to Parliament, and was appointed deputy minister of environment for the new government the next year, a position she holds today.