This study was aimed to find out (1) the students’ frequency of playing yoville game online level of the ninth grade students SMP Muhammadiyah 03 Semarang in the academic year 2012/2013, (2) the vocabulary mastery of the ninth grade students of SMP Muhammadiyah 03 Semarang in the academic year 2012/2013, (3) whether there is a significant correlation between the frequency of playing yoville game online and vocabulary mastery of the ninth grade student of SMP Muhammadiyah 03 Semarang in the academic year 2012/2013.
This study was conducted at SMP Muhammadiyah 03 Semarang from August 7th to August 11th, 2012. The population of this study was the whole students which were choosen by using sample size technique. In collecting the data, the writer used the questionnaire method to determine the student’s frequency of playing yoville game online and test method to measure the vocabulary mastery. Then, the data was analyzed by using descriptive statistics and product moment formula in SPSS 16 (α = 5%, n = 31%, r_table = 0,355).
From the descriptive analysis, it was known that (1) 5 samples have lower level, 4 samples have lower middle level (13%), 4 samples have middle level (13%), 16 samples have upper middle level (52%) and 2 samples have upper level of frequency in playing yoville game online. (2) 6 samples have fail vocabulary mastery (19%), 5 samples have very weak vocabulary mastery (16%), 5 samples have satisfactory vocabulary mastery (16%), 9 samples have very good vocabulary mastery (29,03%) and 6 samples have outstanding vocabulary mastery (19%). While, (3) the correlation analysis between the frequency of playing yoville game onlinne and their vocabulary mastery was 0.933.
From the result above, it can be inferred that generally the ninth grade students of SMP Muhammadiyah 03 Semarang in the academic year have “upper middle” level of playing yoville game online and “very good” vocabulary mastery.

Keywords: correlation, yoville game online, vocabulary mastery