Antibiotic therapy is an essential part of the treatment of sick or injured loggerhead sea turtles (Caretta caretta). Marbofloxacin is commonly used in loggerhead sea turtles at a dose of 2 mg/kg, as in other species. The aim of this study was to increase our understanding of marbofloxacin pharmacokinetics in Caretta caretta. Six healthy turtles were divided in two groups: the intravenous (IV) group (subjects A, B and D) and the intramuscular (IM) group (subjects C, E and F). Each animal received a single dose of Marbocyl® 2%, corresponding to 2 mg/kg of marbofloxacin. The drug was administered by the IV or IM route. After its administration, 13 blood samples were collected at different times: for the IV group at 0, 10, 20, 30 and 45 minutes, 1, 2, 4, 8 and 12 hours and 1, 2 and 2.5 days; for the IM group at 0 and 30 minutes, 1, 1.5, 2, 3, 4, 6, 8 and 12 hours and 1, 2 and 2.5 days. A high performance liquid chromatography ultraviolet light (λ 295 nm) analytical method was used to measure marbofloxacin concentrations in blood. The pharmacokinetic behaviour of the drug was best described by a non-compartmental model. The plasma concentration profiles of marbofloxacin were similar for the two routes of administration and the residual concentrations at 1 day were almost identical. The molecule was detected up to 2.5 days. The apparent volume of distribution was >1 L/kg. The IM route resulted in rapid and complete marbofloxacin absorption (F = 131, 43±12.06 %).