China has reconfigured the global value chains of a wide range of commodities. This includes carrageenan, a polysaccharide extracted from specific types of red seaweeds used as a gelling and thickening agent in a wide range of applications. In the past 20 years, China has moved to centre stage in the global carrageenan processing sector, with wide-ranging implications for seaweed producing nations and farmers. This is especially the case for Indonesia, a pivotal carrageenan seaweeds producer that exports almost all seaweed to China, cemented by large Chinese investments in processing in Indonesia. Despite the importance, there is a dearth of studies on the Chinese domestic industry and associated trade and investment flows. This study fills the gap by triangulating a range of detailed industry, statistical and interview data, in multiple language sources. It finds that Chinese trade and investment linkages is of net benefit to Indonesia but that Indonesian government agencies at both central and local levels can begin to introduce terms in their favour.