The significance of vocabulary knowledge in academic development and having a sufficient vocabulary in language learning cannot be overstated. Research has shown that postgraduate students studying English as a second language (L2) lack vocabulary and require improving it. This research study was conducted to investigate the role of morphological awareness and its relation to productive vocabulary breadth and explore the function of teaching L2 postgraduate students in intervention for improving their productive vocabulary breadth. Thirty L2 postgraduate participants were involved in an intervention. The intervention included 11 sessions of morphological awareness instructions. The students’ morphological awareness was tested using the Morphological Identification Test (MIT) and the Morphological Structure Awareness Test (MSAT), while productive vocabulary breadth was tested using the Productive Vocabulary Level Test (PVLT). A significant relationship was found between morphological awareness and productive vocabulary breadth. The synthetic aspect of morphological awareness was more closely related to the participants’ productive vocabulary breadth than the analytic aspect. The morphological awareness intervention was effective and beneficial in increasing the students’ productive vocabulary breadth. The results may indicate the benefits of teaching and learning morphology to L2 postgraduate students, especially for effective vocabulary building.