Objective: To determine the pharmacokinetics of tolfenamic acid (TA) after different routes of administration [intravenous (IV) and intramuscular (IM), 2 mg kg−1] and doses (IV, 2 and 4 mg kg−1) in red-eared slider turtles (Trachemys scripta elegans). Study design: Randomized experimental trial. Animals: Sixteen healthy red-eared slider turtles. Methods: Turtles were randomly assigned to two groups (n = 8 each). Group 1 received TA at a dose of 2 mg kg−1 IV and then IM, after a washout period of 30 days. Group 2 received 4 mg kg−1 TA IV. A noncompartmental analysis was used to calculate pharmacokinetic variables. Results: No local and/or systemic adverse drug effects were observed in any turtle. Elimination half-life and mean residence time following IM administration at 2 mg kg−1 were significantly longer than those following IV administration. The bioavailability following IM administration was complete. The area under the plasma concentration-time curve, elimination half-life, mean residence time and total clearance were significantly different between the dose groups. Conclusions and clinical relevance: The absence of adverse reactions in the turtles of the study of TA along with the favourable pharmacokinetic properties (the long half-life and the complete bioavailability) of TA administered at the single doses of 2 and 4 mg kg−1 suggest the possibility of its effective use in turtles. However, further studies are required to establish a multiple dosage regimen of TA and to evaluate the clinical efficacy of administering TA.