Many scholars in language learning and teaching agree that vocabulary plays a vital role in a language learning. However, the way the vocabulary is presented to language learners, whether explicitly or implicitly, becomes central discussion in language literature. This study investigated the effect of explicit and implicit vocabulary instructions on students' ESP reading comprehension across cognitive styles. Quasi experimental with pretest-posttest design involving 54 Mechatronics students at the Electronic Engineering Polytechnic Institute of Surabaya was employed in the study. The students were divided into two groups, field dependence and field independence, and received different vocabulary instruction from the teacher (the present researcher). Independent samples t-test and one way ANOVA used in analyzing the data revealed that the group receiving explicit vocabulary instruction outperformed the group receiving implicit vocabulary instruction in comprehending ESP reading. This suggests that explicit vocabulary instruction is more effective in promoting ESP reading comprehension than implicit one. The language practitioners can take it into account in teaching reading, especially in ESP context, to help improve students' comprehension in the reading.