Vocabulary has always been an area of interest and concern for many researchers and teachers alike since words represent "the building block upon which knowledge of the second language can be built" and without them people cannot convey the intended meaning. So that, for the beginners vocabulary really help them to get easy for studying a new language. In other hand, learning vocabulary needs big struggle because it needs memorizing and understanding. Deductive method is one of the ways used to understand well the vocabulary. Deductive method gives chance to the students to be active in class by doing instruction or command from teacher's guidance then they must improve the given vocabulary. Deductive method also makes the students focus on teacher so that the explanation from teacher can be delivered effectively. It is also interesting for the student who has high curiosity and has an analytical style. This research intended to; (1) to describe the holiday program students' vocabulary mastery of HEC 1 Pare Kediri which is taught by deductive method as experimental class; (2) to describe the holiday program students' vocabulary mastery of HEC 1 Pare Kediri which is taught by direct method as control class; (3) to describe the significant difference between holiday program students' vocabulary mastery experimental and control class of HEC 1 Pare Kediri; (4) to describe the effectiveness of deductive method in teaching vocabulary mastery of holiday program at HEC 1 Pare Kediri Quantitative was selected as a research approach, whereas the research design used was post-test only control group design. This research used two classes which became experimental group and control group. The instrument used was a written test which resulted score of students' achievement. The mean score of the students' vocabulary mastery in experimental class is 83.89 and it means the score in very good category. Meanwhile, for control class, the score is in good category and has mean score 79,11. Independent- samples t-test with an alpha level of 0.05 was used to investigate the significant difference between both groups. The analysis revealed that the experimental class outperformed the control class in vocabulary mastery with t = 2.931, df = 70 and P = .005 and 95% confidence interval ranging from 1.527 to 8.028. The result of t-test shows the mean difference is 4.778 with sig. (2-tailed) value .005. The value indicates that the significant difference between two groups is found. Thus, it can

Keyword: Deductive Method, Vocabulary Mastery.