This research was aimed at analyzing the comparison of vocabulary
mastery between high and low reading interest students. A descriptive quantitative
method was used in this research. The sample of the research was 34 tenth grade
students dividing into two groups which were high interest group (17 students)
and low interest group (17 students). Data was collected by a test instrument
which was designed with five vocabulary aspects that were based on Hughes
(1989) and Harmer (2001), and the questionnaire instrument was based on Arisma
(2012) and Santrock (2004). The technique of data analysis was non-parametric
statistic using Mann-Whitney Test Analysis because of the normality test result.
The result of normality test proved that the score distribution was not normal
since sig. counted is lower than sig. level of 5% (0.020 < 0.05). The result showed
that the probability value (p value) of Mann-Whitney Test was 0.00 that was
proved lower than the significant level 5% (0.05). Thus, there was a significant
result. Moreover, the significant result was strengthened by the average score of
the vocabulary test on each aspect which showed that high interest group got
higher average score than the low group (71.9% > 46.6%). In brief, it can be
concluded that the working hypothesis (Ha) was accepted, or in the other word the
higher students’ interest in reading was the better vocabulary mastery will be.