Politeness is influenced by cultural perspectives across cultures. Studies of politeness strategies in intercultural communication have often highlighted cultural speech acts in conversation discourse in various situations. This study investigates cultural politeness between Thai students and an expatriate lecturer and its features of Thai and Western speech acts in an online forum, a learning platform which has recently been introduced in Thai EFL university context. Due to variation in the cultural politeness of interlocutors, Thai students' politeness strategies are possibly misinterpreted in another culture, or they may fail to communicate illocutionary force in intercultural communication. The participants were 146 Thai EFL undergraduate students and an American lecturer, who was teaching an English and American cultural background course. The online entries were theoretically analysed and the findings were supported with data from focus-group interviews. The results show that the student participants were most likely to use Positive politeness, followed by Bald-On-Record politeness, Negative politeness and Off-Record politeness strategy when posting online entries to the lecturer. For features of Thai-Western politeness and speech acts, the respect phenomenon affected the language use of politeness strategies in posing intercultural difficulties. The analysis contributes to the overview of Thai and Western features of cultural politeness in a Thai online EFL setting.