It is widely accepted that the disposal construction markers JIANG and BA are grammaticalized in serial verb construction (SVC). However, the motivations and the processes of grammaticalization are still unclear. This paper will attempt to clarify and exemplify the processes by proposing that JIANG's persistence of co-occurring with SVC, the semantic bleaching of JIANG from ”to lead” to ”to take”, and the decline of the pronoun ZHI in the SVC are three motivations for the grammaticalization.