Fluid intelligence is known to correlate with various cognitive abilities, but its impact on prospective memory (PM), particularly in tasks with varying cognitive demands, remains largely unknown. In a study with N = 178, we thus investigate how fluid intelligence and attentional control relate to PM. Participants performed a two-back task with words as the ongoing task and participants had to press a special key whenever rarely occurring PM cues were presented in the context of the two-back task. PM cue detection difficulty was manipulated by using either two specific words or two specific letters as cues. Fluid intelligence was assessed with the short form of the HeiQ, a validated figural matrix test, and attentional control was assessed with the Three-Minute Squared Test, which includes Stroop, Flanker, and Simon tasks. Data collection is ongoing, but preliminary analyses show a significant difference in PM performance, with participants performing better when cues are easier to-be-detected. Furthermore, a positive correlation between attentional control and PM performance was found for the difficult to-be-detected but not the easy to-be-detected cues. When data collection is finished, we intend to test the hypothesis that the relationship between fluid intelligence and PM is mediated by attentional control when PM cue detection is attention demanding.