Abstract: About 4500 participants gathered in St. Louis，Missouri，USA from 1 to 7 August, 1999 for the 16th International Botanical Congress —the last grand meeting of the world's botanists in the 20th century. The discussions ranged from the conservation of botanical diversity to the challenges and opportunities: plant science in the 21st century. Twenty one Symposia focused on six disciplinary areas, those are, Botanical diversity: systematics and evolution;Ecology,environment and conservation; Structure,developme nt and cellular biology; Genetics and genomics; Physiology and biochemistry; Human uses of plants: economic botany and biotechnology. An introduction on the congress was given and especially on the botanical diversity conservation in detail . And a few suggestions on China's plant science in the future was put forward.