This study examined the effect of mobile-mediated dynamic assessment on reading comprehension and reading fluency skills of Iranian L2 learners. With 50 Iranian L2 learners, randomly assigned to the experimental and control groups, a pretest-posttest control group design was used. Whereas the control group received traditional instructor translation of reading materials, the experimental group received mobile-mediated dynamic assessment including interactive reading tasks mediated by the teacher via a mobile application. Pre- and post-assessment of L2 reading comprehension and reading fluency was achieved by means of researcher-made tests for data collecting. Conducting independent samples t-tests, the results of the study showed that, in both reading comprehension and reading fluency, no difference existed between the two groups on the pretest. However, on the posttest, the experimental group outperformed the control group on both measures of reading comprehension and reading fluency demonstrating the effectiveness of mobile-mediated dynamic assessment in improving L2 reading skills. The design and execution of the study benefited from theoretical foundations derived from mobile-mediated language learning and dynamic assessment. The results of the study add to the body of knowledge by showing the possibility of mobile-mediated dynamic assessment as a creative approach to raise reading competency of L2 learners. The implications for language teachers, policy makers, syllabus design, and materials development are discussed and recommendations for future studies to investigate the efficacy of mobile-mediated dynamic assessment in several instructional environments are offered.