This paper investigates the factors that influence the adoption of RSPO and Thai-GAP certification by oil palm smallholder farmers in Thailand. A random sample of 77 RSPO certified, 108 non-certified RSPO, 87 Thai-GAP certified, and 67 non-certified Thai-GAP smallholder farmers were interviewed to investigate the factors explaining the RSPO and Thai-GAP scheme adoption, respectively. The logit model was used to analyse the relationships between the adoption and the decision-making factors of the farmers. The results show that membership of farmer groups, the goal of the scheme, and trust in the scheme are the most significant factors affecting the adoption of RSPO certification. Scheme payments have a negative influence on adoption. In case of Thai-GAP, the results show the scheme payment, the image, concerns about the quality of land and water, and trust in the scheme are the most significant factors affecting the adoption. Finally, these findings suggest new factors may be attributed to several issues, including trust in the scheme, membership of farmer groups, the scheme’s goal, and trust in the scheme are the most significant. Designing and extension in influencing factors may play multiple roles in driving smallholder farmers to adopt sustainable certification schemes. This finding repeats that the usability of sustainable certification schemes in developing countries needs to be mobilised around a particular socio-cultural context. Including, understanding the factors affecting smallholder farmers’ intention to adopt Thai-GAP or RSPO certification is very important to plan and promote these schemes among other farmers and transform the current cultivation practices into more sustainable palm oil production.