At a stage ealier than Proto-Min, the pronunciation of some words of the Jing (精) initial group had shifted to the Zhang (章) initial group. This paper designates this merger as 'Jing (精) initial group shifts to Zhang (章) initial group'. Based on the study of six words, i.e. '笑 (to laugh)', '像 (to resemble)', '蓆 (mat)', '惜 (to love dearly)', '粟 (grain)' and '筅 (pot-scouring brush)', the paper defines this shift as 'a phonological change of dental fricatives which occur before the medial *i to aspirated postalveolar affricates'. However, this definition involves many exceptions and counterexamples. In addition to the Min dialect, there are some isolated residues of 'Jing initial group shifts to Zhang initial group' in the Chuqu (處衢) and Wuzhou (婺州) subgroups of the Wu dialect. These residues further reveal the close historical relationship between the Min dialect and the Chuqu and Wuzhou subgroups of the Wu dialect and indicate that the origin of 'Jing initial group shifts to Zhang initial group' is very archaic also.