Background <p>Ultra-processed food companies in Thailand have rapidly expanded, and they play an important role in the domestic economy and public policy. These companies influence policy-making by building networks with political authorities and using various strategies to pursue their interests. Increased consumption of ultra-processed foods has been shown to be strongly associated with obesity and other non-communicable diseases (NCDs), which are a growing public health concern in Thailand. This study investigated the commercial determinants of health (CDOH) strategies of the major ultra-processed food companies in Thailand.</p> Methods <p>This study employed document review to classify CDOH’s strategies of ultra-processed food companies in Thailand. The authors searched publicly available information by 15 ultra-processed food companies, including both national and transnational companies, between January 2019 and December 2024. In addition, 30 semi-structured interviews were conducted with field experts to provide additional insights to support the findings from the document review. Thematic analysis was used to interpret the data.</p> Results <p>National ultra-processed food companies in Thailand employ all seven strategies of CDOH, namely: (1) Political, (2) Scientific, (3) Marketing, (4) Supply chain and waste management, (5) Labour and employment, (6) Financial, and (7) Reputation management strategies. Transnational companies employed all but one of the seven strategies (labour and employment).</p> Conclusions <p>The wide array of CDOH strategies used to shape public policy and opinion may hinder efforts to protect the health of Thais from obesity and diet-related NCDs. To counter this, the authors recommend systematic monitoring of CDOH strategies, stronger accountability for the ultra-processed food companies, mandatory lobbyist registration, stricter management of conflict of interest between government officials and food companies, and strict enforcement of relevant legislation.</p>