This paper intends to study the tonal variation between tone 3a (i.e. Yinqu) and 2b (i.e. Yangshang ) as observed in modern Hong Kong Cantonese. Two social variables will be involved: age and gender. In the light of apparent time hypothesis, the findings help to determine whether such a variation is a result of an on -going sound change. The results reveal that there are two on -going tone changes in opposite directions, namely, 3a > 2b and 2b > 3a, and so far the former seems more forceful than the latter. The sound changes are carried out by lexical diffusion, and the unit of diffusion is more likely to be disyllabic and other polysyllabic compound words rather than monosyllabic morphemes. The gender variable, on the other hand, is found ...