Metabolites of ethoxyquin (EQ, 1,2‐dihydro‐6‐ethoxy‐2,2,4‐trimethylquinoline) in the urine of sheep and rats were separated and identified by gas chromatography‐mass spectrometry (GC‐MS). Sheep were given diets containing EQ or EQ · HCI (0.5% of total diet) and urine samples were collected for the first 24 h and for another 24‐h period after 12 d of feeding. Rats were given EQIcorn oil (0.08 g EQ/d/ rat) orally for 7 d and urine samples were collected at ambient temperature for a 24‐h period following 6 d of dosing. The urine samples were extracted with ethyl acetate at pH 5, and the concentrated extracts were analyzed by GC‐MS. Ethoxyquin was identified in all sheep urine samples collected during the first 24 h of feeding, and EQ and hydroxylated EQ were identified in all urine samples collected after 12 d of feeding. In contrast, EQ, hydroxylated EQ, and dihydroxylated EQ were identified in urine collected from rats fed EQ for 7 d.