The park, a 22,918ha area, harbours a diversity of flora with 256 species of vascular plants, of which some species were recorded for Melaleuca peatswamp forests for the first time such as two terrestrial orchids Spiranthes sinensis and Eulophia graminea. The natural vegetation was classified into 10 types, belonging to four main classes: Melaleuca forests, seasonally inundated grasslands, permanent swamps and vegetation along canals and streams.

The forest and wetlands at U Minh Thuong support many rare animal species and the highest bird species richness of any of the sites visited. To date, 187 bird species have been recorded at U Minh Thuong, including nine globally threatened or near-threatened species: Oriental darter, Spot-billed pelican, Painted stork, Lesser adjutant, Black-headed ibis, Glossy ibis, Greater spotted eagle, Grey-headed fish eagle and Asian golden weaver.

U Minh Thuong also supports globally significant congregations of a number of commoner waterbird species, including Purple swamphen, Little cormorant, Purple heron, Glossy ibis. For these reasons, U Minh Thuong qualifies as an Important Bird Area.