This work attempts to examine the frequently used Sentence-Final Particle (SFP) wo3 in Hong Kong Cantonese synchronically and diachronically. In the past, most experts treated wo3 and another particle bo3 as variant forms, with the former being the result of sound change from the latter. In order to investigate the development of wo3, the early materials, movies and the university corpus are employed for the collection of language examples. It is found that in terms of their meanings and functions, wo3 and bo3 were distinctly separate at the very beginning. The observation of the increase and decrease in the frequency of use of the two SFPs in the past one hundred years makes it evident that while the usage of one prospers, the other declines. Regarding the formation of the multi-functional particle wo3, a grammaticalization chain is shown in this work to reflect its historical development, and its current situation is thus made clear with the analysis under the principles of unidirectionality, coexistence and preservation. The theories of evidentiality and subjectivity are brought in to differentiate wo3 from another SFP wo5 in the last part of this work.