This paper examines the nature of categorical perception (CP) effects in Mandarin and Dutch adult listeners through identification and discrimination tasks using lexical tonal contrasts and through the CP index analysis. In identification tasks, Mandarin listeners identify tones in accordance with their native tonal categories whereas Dutch listeners do so based on acoustic properties. In discrimination tasks, Dutch listeners outperform Mandarin listeners especially in tonal steps on the continuum falling within the Mandarin tonal category boundary, whereas Mandarin listeners display high sensitivity in discrimination of stimuli falling across the native boundary. The CP index analysis shows a higher degree of CP in Mandarin (categorical perception) than in Dutch (psycho-acoustic perception) listeners.