There is a strong association between vaginal and/or amniotic fluid Ureaplasma spp. colonisation and risk of preterm birth (PTB). The novel fluoroketolide antibiotic, solithromycin (CEM-101), is highly effective against Ureaplasma spp. and evidence from pregnant sheep suggests that, unlike most macrolide antibiotics, it readily crosses the placenta. Solithromycin has two bioactive metabolites, CEM-214 and N-Acetyl-CEM-101 (NAc-CEM-101) which have been shown in a pregnant sheep model to accumulate in the amniotic cavity following maternal administration. This has the potential to enhance the drug’s effectiveness for treatment of in utero infections. However, the antimicrobial activity of these metabolites against Ureaplasma spp. has not been established. The effects of solithromycin, CEM-214, NAc-CEM-101 and (for comparison) azithromycin were tested on a collection of 100 clinical Ureaplasma spp. isolates from the United Kingdom and Australia using a modified 96-well broth microdilution method. The mean minimum inhibitory concentration (MIC) values (µg/mL) observed for the combined cohort were: solithromycin, 0.06; CEM-214, 0.29; NAc-CEM-101, 0.37; azithromycin, 1.99. One bacterial isolate showed resistance to azithromycin (MIC 16 µg/mL) and also exhibited a greater MIC against the other compounds tested. Solithromycin showed 34-fold greater activity against susceptible Ureaplasma spp. isolates than azithromycin, while CEM-214 and NAc-CEM-101 possessed approximately 22% and 17% activity of solithromycin, respectively, significantly greater than that of azithromycin. Solithromycin and its two metabolites exhibit potent activity against Ureaplasma spp. This suggests prolonged activity of the drug post-metabolism and has important implications for the treatment of infection-associated PTB.