Writing is usually considered the most challenging skill for the majority of students in the Vietnamese context. Several previous studies revealed that the instruction of morphological knowledge has positive impacts on expanding students’ vocabulary and indirectly improves the quality of academic writing. This current study was implemented in order to investigate EFL intermediate students’ attitudes towards the impacts of teaching morphological knowledge on the degree of lexical complexity and the quality of academic essays in the context of an English language center in the Mekong Delta. This 14-week experimental research employed the use of pre-questionnaire and post-questionnaire, with the participation of two groups of EFL intermediate students who were studying at a similar level and progress. The results indicated that EFL intermediate students in the experimental group had positive attitudes towards the impacts of teaching morphological knowledge on the degree of lexical complexity and the quality of their academic essays throughout the research period, whereas no positive changes regarding attitudes could be found within the ones in the control group. From that, several recommendations and pedagogical implications were drawn with the attempt to contribute to the innovation of teaching vocabulary and teaching writing in the context of secondary schools and high schools in the Mekong Delta.