Dynamic assessment is an approach primarily based on sociocultural theory of mind with the objective of combining instruction and assessment. In this approach learners’ development is simultaneously assessed regarding their Zone of Proximal Development. The present study was intended to investigate the effect of Mobile-Assisted Dynamic Assessment (MADA) on IELTS writing task one and also the EFL learners' perception to such approaches toward language learning. In order to achieve the aim of this quasi-experimental study, a social networking application, namely Telegram was applied on mobile phones. Based on the scores on the Oxford Quick Placement Test, twenty-three Iranian advanced-level EFL learners out of a population of 40 students participated in this study. An intact group went through a pre-test- treatment-post-test process. In the end, the participants were interviewed for their perceptions on mobile assisted dynamic assessment which was used to assess their writing skill. The results of the data analysis revealed that the participants experienced improvement in their writing after the treatment and obtained a significant increase in their scores of the post-test, and they benefited from the process of dynamic assessment through online mobile-learning environment. They further had a positive perception towards MADA.