For many students of English, whenever they think of vocabulary, they think of learning a list of words with meanings in their native language or sometimes they are asked to memorize it. Online game as media in learning process is chosen to help the teacher explain the lesson. Online game (Magic rush)or video game is a part of life style. Many people play it every time and the players come from many countries in this world. In this research, the researcher tries to find out the effectivenes of online game in teaching vocabulary at the seventh grade of MTsN 1 Kediri. By using online game, students are expected to master the vocabulary in descriptive text as their basic competence in curriculum. This research intended to; (1) To describe the students' vocabulary mastery in experimental class,(2) To describe the students' vocabulary mastery in control class,(3) To analyze the significance different of students' achievement,(4) To analyze the effectiveness of online game in teaching vocabulary. Quantitative was selected as a research approach to respond research question which require a numerical data. The research design selected is Quasi Experimental by Nonequivalent group, post-test only. This research used two classes which became experimental and control class. The subject in this research is students from the seventh grade of MTsN 1 Kediri. It is used two classes as the experimental class (VII C) and control class (VII D). The instrument used was multiple choise test.the formula follows
t = X1 - X2
(n1-1) S1/2 + (n2 - 1) S2/2 (1/n1 + 1/n2)
n1 + n2 - 2
The result of this research; (1) the mean score of experimental class is 88,29, (2) the mean of control class is 83,92, (3) Independent sample t-test with an alpha level of 0,05 was used to investigate the siqnificant difference between both group. The analysis revealed that the experimental group outperformed the control group in vocabulary achievement with 1 =2,227, df =73, P = 0,29 and 95% confidence interval ranging from .459 to 8.282. The result of t-test shows the mean difference is 4,371 with sig. (2 -tailed) value 0,29. The value indicates that the significant difference between two groups is found. (4)Thus, it can be concluded that Online Game (Magic Rush) is effective in teaching and learning of English vocabulary in descriptive text. After the researcher found the result, it is recommended for; (1)The English teachers in order to use online game (Magic Rush) as media in teaching vocabulary in order that student get interesting way to learn english. (2) The students, it is suggested to

Keywords: Online Game, Teaching Vocabulary