The aim of this research is find out the effectiveness of guessing word game. This research conducted at MTs Syamsul Huda Kedungreja, Cilacap in academic year 2011/2012.
The treatment was carried out in August 2011. The method in this research was quasi experiment especially non-equivalent. The total sample of this research was 92 respondents. The respondents were divided into two classes; there were class A as control and class B as experiment. The treatment was given for the experimental class. In collecting the data, the writer used test as an instrument. The test was done twice; the first test was pre-test and the second was post-test. After getting the data, the writer used t-test to analyze the data collected.
Based on the result, t-test was 3.083 and the result of t-table with degree of freedom 1.662. t-test is higher than t-table (3.083>1.662). Therefore, it can be concluded that Guessing Word Game is effective for teaching vocabulary.