This thesis examines the perfective marker dao in the Nanjiang dialect and traces such usage in history. The morpheme dao in the language variety can be used as perfective marker in a variety of constructions, whereas in the Early Modern Chinese period dao's perfective use was relatively limited: measure phrases are employed to modify either the main verb or the object of a transitive verb. By reflecting on semantic changes of dao taking place in Early Modern Chinese, we suggest that relativization is a key step in the development of dao as an aspectual marker, that is, V(erb) dao O(bject) may be a direct reanalysis of V dao (as a modifier) + Head Noun, different from what is assumed in the literature, the substitution/analogy hypothesis about how the object of a transitive verb is placed after the post-verbal particles like le.