Attention to vocabulary and finding appropriate strategy to learn new vocabularies has always been challenging for learners or even teachers. Researchers' consideration to vocabulary has been growing since mid. 1980s. In this regard, various researchers and teachers stated one or some instructions are more helpful for learners. This study is an attempt to investigate the effect of Isolated, Integrated, and Synonym Generation vocabulary instruction on writing skill among Intermediate EFL learners. For this purpose, 77 male and female learners were chosen through administering a piloted Preliminary English Test. They were then divided into three experimental groups and each of the groups was taught vocabulary through one of the mentioned instructions. At the end of the study, all participants were given a writing test. One-way ANOVA on the posttest demonstrating that the learners in the Integrated and Synonym Generation groups benefited significantly in terms of improving their writing ability.