The current study examined the effects of task condition (TC; single vs. dual) and proficiency level (PL) on self-monitoring of second language (L2) speakers. Data were collected from sixty-six female L2 learners of English performing two speaking tasks under two task conditions. While performance in the single-task condition involved only narrating a picture-based oral narrative, the dual-task condition involved performing the same oral narrative as well as a secondary task. Factor analysis, MANOVA, and two-way ANOVAs were used to examine the effects of PL and TC on a range of self-monitoring measures. The results indicated that the higher proficiency learners made significantly fewer filled pauses, repetitions, and hesitations, and a higher ratio of error correction and error-free clauses than the lower proficiency learners. These results suggest that with the development of proficiency L2 learners' performance becomes more fluent, and a more active and effective monitoring process seems to be at work. Compared to the single-task condition, performance in the dual-task condition led to significantly more repetitions implying the increased demand of TC triggers more dysfluency. These results are discussed in relation to the L1 monitoring models.