The present study investigates dative alternation and various uses of gei in Mandarin Chinese. We first examine previous studies on the syntactic properties of double object constructions and dative constructions, and then propose our analyses of these two constructions. Specifically, we argue against a syntactic derivational relation between them and further suggest that the linking between thematic hierarchy and argument structure is a general principle, rather than a rigid rule as claimed by Baker (1988) and Larson (1988). Furthermore, following Ting and Chang (2004), we suggest that gei in Mandarin has undergone categorial change and that such categorial change is witnessed through its versatile syntactic behavior. The grammaticalization path of gei in Mandarin conforms to the studies in functional grammar and the historical development of the verb. Other related issues, including the V-gei formation and source double object constructions, are also addressed in this thesis.