The agency battled incumbent Freeway and Publicis, which was awarded the brand's Singapore business in October last year, for the brief.
FCB Hong Kong managing director Dionne Kung said: "(Osim) was looking for an agency to give it more of an all-rounded, strategic and creative solution. Osim is quite active in Hong Kong and the brand is highly exposed.
"We are starting work on a number of projects. The challenge now will be how to uplift the brand image and how to bring the product to life to consumers. The majority of Osim's products relate to daily health."
MindShare continues to handle media, with Octagon as Osim's public relations agency.
In a separate development, FCB Hong Kong has been awarded the creative brief for a new shopping mall set to open in East Kowloon in December 2006.
Developer Kerry Properties appointed the agency following a pitch against Euro RSCG and local shop Hotdog.
Kung noted: "The pitch process wasn't long, just one round of presentations. It's going to be a major mall in terms of size, however, it's too early to talk about the mall's concept."