The aims of the research were: (1) to know how good is the students‘ mastery of
new vocabulary in reading Jakarta Post Articles and (2) to know kinds of
vocabulary problems in Jakata Post Articles. The sample of this research was 44
students; the researcher took 30% from the population of fifth semester students
of English Department University of Muhammadiyah Purwokerto. The data was
collected through test. The data were analyzed by using descriptive study. The
writer took the data on December 24th 2014 at the fifth semester students of
English Department University of Muhammadiyah Purwokerto. After the data had
been analyzed, it was got three catergories of individual students‘ mastery
included very good, good and fair. Two students (4.55%) belonged to very good
category, 29 students (65.90%) belonged to good category, and 13 students
(29.55%) belonged to fair one. The mean of the students‘ mastery was 67.77. In
conclusion, the fifth semester students of English Department University of
Muhammadiyah Purwokerto master new vocabulary well and could be classified
belonging to good. There were four kinds of vocabulary in Jakarta Post given
problems for the students, but the most problem was vocabulary mastery of noun
(66.76). The other problem was the students‘ mastery in the meaning of the words
(77.67%).