Cantor coding has been theoretically proposed as an excellent way to encode sequential information in the brain. Empirical verification has been successfully given for the dynamical nature of the Cantor coding in experiments using hippocampal slice preparations. However, because these studies adopted artificial electrical stimulation for inputs, it remains unanswered as to whether brain really uses this coding scheme. In this study, we examined the Cantor coding in vivo in HVC (a song nucleus) of Bengalese finches, as the HVC is responsible for processing complex sequence of song syllables. We recorded multiple single-unit responses to acoustic stimuli that were composed of randomized sequences of syllables. Analyses of neuronal activities revealed that auditory responses of single HVC neurons coded sequences of multiple syllables (3 or more), suggestive of the hierarchical dependency that is a necessary condition of the Cantor coding. Further studies will shed light on how the Cantor coding could be implemented in biological system.