There are six recognised Ureaplasma species, They have a G+C content of 27 - 30 mol%, and a genome size ranging between 0.76 - 1.17 Mbp, and cholesterol is required for growth. A defining characteristic of the genus is that they perform urea hydrolysis.
It is now recommended that some strains originally classified as Ureaplasma urealyticum should be treated as a new species, U. parvum.