The aim of this research was to find out the effectiveness of four corners technique in developing speaking skill at the eleventh grade of SMK N 1 Banyumas 2014/2015. This research used quasi experimental research with the students of eleventh grade of SMK N 1 Banyumas as the population. The total sample of this research was 60 students, and the sample of experimental and control class was XI AK 3 and XI TKJ 1 which consisted of 30 students. Four Corners technique was given in experimental class, while control class was taught by using discussion technique. To collect data, there were two types of test that were used, those were pre-test and post-test. The test was focused on the language expression of asking and giving opinion in the form of dialogue. After the data was obtained, it was analyzed by using t-test. The result was 3.5767, and it was higher than t-table (1.6715) at
with df = 58. Based on the pre-test and post-test result, the score of each aspect of speaking namely fluency, comprehension, grammar, vocabulary and pronunciation increased and showed the significant increase. Based on the description above, it could be concluded that Four Corners technique was effective to develop speaking skill.