The aim of this research was to know whether monopoly game is effective or not in teaching conditional sentence at SMK Diponegoro Majenang. The method used was experimental method. The population of this research was twelve grade students of SMK Diponegoro Majenang. The writer chose two classes as samples, 3 Ap 2 as experimental class and 3 Ap 1 as control one. The research was carried out from 21st March until 2nd April 2011. The writer used pre-test and post-test to find the data. T-test was used to analyze it. Having analyzed the data, the writer revealed that the student’s ability in experimental class was higher than control one. There was positive effect in teaching conditional sentence through monopoly game at SMK Diponegoro Majenang. The t-test result was 2.748 and t-table in degree of freedom 78 at the significant 0.05 was 1.664. The hypothesis was accepted because t-test was higher than t-table (2.748 > 1.664). It means that monopoly game is effective for teaching conditional sentence.