L2 sounds present different kinds of challenges to learners at the phonetic, phonological, and lexical levels, but previous studies on L2 tone learning mostly focused on the phonetic and lexical levels. The present study employs an innovative technique to examine the role of prior tonal experience and musical training on forming novel abstract syllable-level tone categories. Eighty Cantonese and English musicians and nonmusicians completed two tasks: (a) AX tone discrimination and (b) incidental learning of artificial tone-segment connections (e.g., words beginning with an aspirated stop always carry a rising tone) with synthesized stimuli modeled on Thai. Although the four participant groups distinguished the target tones similarly well, Cantonese speakers showed abstract and implicit knowledge of the target tone-segment mappings after training but English speakers did not, regardless of their musical experience. This suggests that tone language experience, but not musical experience, is crucial for forming novel abstract syllable-level tone categories.