OBJECTIVE To determine the predominant thromboxane (TX) metabolite in urine of healthy cats, evaluate whether the method of sample collection would impact concentration of that metabolite, and propose a reference interval for that metabolite in urine of healthy cats. ANIMALS 17 cats (11 purpose-bred domestic shorthair cats, 5 client-owned domestic shorthair cats, and 1 client-owned Persian cat). PROCEDURES All cats were deemed healthy on the basis of results for physical examination, a CBC, serum biochemical analysis, urinalysis, and measurement of prothrombin time and activated partial thromboplastin time. Voided and cystocentesis urine samples (or both) were collected. Aliquots of urine were stored at −80°C until analysis. Concentrations of TXB2, 11-dehydroTXB2, and 2,3 dinorTXB2 were measured with commercially available ELISA kits. Urinary creatinine concentration was also measured. RESULTS 11-dehydroTXB2 was the most abundant compound, representing (mean ± SD) 59 ± 18% of the total amount of TX detected. In all samples, the concentration of 11-dehydroTXB2 was greater than that of 2,3 dinorTXB2 (mean, 4.2 ± 2.7-fold as high). Mean concentration of 11-dehydroTXB2 for the 17 cats was 0.57 ± 0.47 ng/mg of creatinine. A reference interval (based on the 5% to 95% confidence interval) of 0.10 to 2.1 ng of 11-dehydroTXB2/mg of creatinine was proposed for healthy cats. CONCLUSIONS AND CLINICAL RELEVANCE In this study, 11-dehydroTXB2 was the major TX metabolite in feline urine. Measurement of this metabolite may represent a noninvasive, convenient method for monitoring in vivo platelet activation in cats at risk for thromboembolism.