This article analyzes the permeation from the dominant dialect, Mandarin, to the Shanghai urban dialect, based on the change of xiyin syllables having the Cong initial. Combining random sampling and anonymous observation methods we investigated variations in consecutive age groups of speakers. Statistical analyses reveal that the Shanghai urban dialect is moving toward Mandarin. Under the pressure of the dominant dialect the change is in progress at the population, pragmatic, and lexical levels. These changes are explained within the framework of current theories of language change.