Online forum as media for exchange information that can be accessed online by the public (citizen), especially cooking information. Despite the citizen can obtain various information through online forums, very little is known about factors affecting the effectiveness of online forums in cooking information. This study, therefore, seeks to analyze what factors can influence online forum's effectiveness as knowledge sharing media in increasing people's knowledge and cooking performance. There are four indicators used in this study, knowledge sharing, knowledge application, knowledge creation, and transactive memory system (which refers to three-point: specialization, credibility, and coordination). The survey was taken place and obtain 174 respondents as samples. Structural Equation Modelling (SEM) was conducted with SmartPLS tools to test this research. The result of this study concludes that knowledge application, knowledge sharing, and knowledge creation significantly influence knowledge and cooking performance by using transactive memory systems (TMS) theory. © 2020 IEEE.