This study aims to explore how Taiwanese EFL college students plan and execute interlanguage compliments by uncovering their cognitive processes. Two male and two female learners took part in four complimentary situations in open-ended role plays with English native speakers. Retrospective verbal report was conducted immediately after the role plays to elicit the process data regarding cognition (information attended to) and the language of thought. Retrospective data indicated that, during the planning and execution of compliments, the respondents focused on compliment planning, context planning, conversational management, politeness, and prior experience or knowledge. Moreover, the students tended to consult both Mandarin and English in the planning and production phases. The native language performed more functions than the target language. Additionally, the learners employed several communication strategies to search for, retrieve and select language forms, including din in the head, awareness of using a monitor, self-debate before selection, partial delivery of a thought, code switching and message abandonment. In the present study, retrospective verbal report is instrumental in revealing learners' cognitive processes in the planning and production of speech acts which cannot be elicited from the performance data.