This article presents the findings of a corpus based research that investigated Malaysian ESL learners' use of modals in two written tasks. The aim of the study was to investigate the distribution and functions of modals used in the students' writing. The research design comprised a qualitative technique through discourse analysis supplemented with some descriptive statistics derived from a concordancer which identified modals used by the students at two different levels. The findings showed that the preferred modals for the two levels are modals "can", "will" and "could" which were used to express ability and certainty. Modals of probability/possibility showed lower frequencies of use in the writing. Also, students at the lower level were less competent in using past form modals as compared to those at the higher level. This study indicates that the students were able to perceive the conceptual meaning of each modal and their communicative function.