The ability of cats to discriminate changes in the second formant of the vowel /ε/ was examined across a range of stimulus levels. Cats were trained to press and hold down a lever to produce a pulsed train of the standard vowel /ε/, and to release the lever only when a variant of /ε/ occurred. Six synthetic variants of /ε/ had the same first and third formants (F1andF3), but with the second formant (F2) located between 1700 and 2000 Hz. All stimuli were tested at levels of 10, 30, 50, and 70 dB SPL. Average difference thresholds for changes inF2(ΔF2) of the vowel /ε/ ranged from 87 to 36 Hz across levels of 10 to 70 dB SPL, and were only slightly above those of humans. Further, the ΔF2values were lower than pure‐tone ΔFvalues in the same frequency range, whereas humans exhibit higher ΔF2values than pure‐tone ΔFvalues in the same frequency range. Changes in the second formant in a negative direction (downwardF2shifts) were also found to be more difficult to detect than upwardF2shifts. These results suggest that, compared to pure tones, cats are better able to discriminate small changes in more complex, vowel‐like stimuli.