This study investigated the effectiveness of three kinds of vocabulary instruction. Seventy learners in the classes of English for Specific Purposes (ESP) were divided into three different groups receiving different instructions: Focus on Form Instruction (FoF) (Dictogloss task), Focus on Meaning Instruction (FoM) (Reading and Discussion task), and Focus on Forms (FoFs) Instruction (Word lists). The first two groups were experimental groups, and the last group was control group. The results of this research indicated that learners in FoF group achieved significantly higher scores than those in FoM and FoFs. Also, learners' scores in FoM group were significantly higher than FoFs group. These findings were justified by main features of FoF tasks (dictogloss) including depth of processing hypothesis, discovery learning, pushed output, noticing hypothesis, awareness raising, negotiation, collaboration, and motivation.