This study investigated whether the modality effect of content presentation modes on students' cognitive load and listening comprehension depends on the moderating effect of the learners' language proficiencies in a mobile learning context. One hundred and sixty-two students majoring in English in a technology university used personal digital assistants (PDAs) as the learning tool for a mobile listening comprehension activity. Participants were randomly assigned to one of two presentation modes: (1) a single mode in which students were engaged in auditory materials only and (2) a dual mode in which they were exposed to audio and textual inputs simultaneously. Hierarchical regression was employed to examine the moderating effect of the learners' proficiencies. The results confirmed the moderator role of English proficiency on cognitive load: students with lower proficiency appeared to be more perceptive of the text aid. However, the moderating effect was not obtained on the task performance in that students provided with the dual mode outperformed their single mode counterpart across the proficiency level. This study recommends that written text be displayed when students are engaged in a mobile English listening comprehension task to reduce learners' cognitive load. The study also provides pedagogical implications for mobile language learning. (Contains 9 tables and 5 figures.)