This study examines tone mergers in Hong Kong Cantonese from the perspective of variationist sociolinguistics. It approaches the issue of whether Cantonese has six or nine tones by focusing on two ongoing tone mergers: (1) the merger of yin qu T3 and yang qu T6, and (2) the merger of lower yin ru T8 and yang ru T9. Speech data from fifty native Cantonese speakers in Hong Kong were collected and analyzed. The change routes and constraint patterns of the two mergers were compared and found to be similar. The results support the six-tone system for Hong Kong Cantonese. This study serves as an example of how the variationist approach can be used in phonological debates.