Developing countries, including some 30 heads of government and representatives of more than 100 nations -- about two-thirds of the world's countries -- gathered to demand a more fair new world order.
But Morales, a leader of Latin America's hard left and the group's current president, called for "eliminating world hierarchies" altogether.
"The UN Security Council should be eliminated, because it has encouraged wars and invasions by imperial powers to appropriate natural resources of invaded countries," he said.
Morales also emphasized that integral development includes "not only a balance between human beings, but balance and harmony with Mother Earth."
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Other dignitaries at the event include the presidents of Venezuela, Ecuador and Cuba.
The Santa Cruz meeting marks the 50th anniversary of the body's founding, with the group having grown from 77 developing countries to 133.
The summit will close with a document that Bolivia's Vice President Alvaro Garcia described as "the first draft of the post Millennium Development Goals," a set of UN goals that are approaching their 2015 expiration date.
The world is still well short of fulfilling the original eight Millennium goals, which include a call to halve the number of people living in extreme poverty.
UN Secretary General Ban Ki-moon, who opened the summit, emphasized the need to accelerate efforts to meet the goals and said the destiny of billions of poor people and the state of the planet depends on the countries' work.