The purpose of this research was to improve the students` writing skills
through writing diary. This research was conducted at the first grade of SMK
Komputama jeruklegi. This research belongs to classroom action research. the
researcher took two cycles and used three instruments to collect the data. The
instruments were test, observation and questionnaire. Based on the result of the
research, the test showed the significat improvement. It can be seen from the
mean of the students` scores. In cycle 1, the mean of the students` scores in Pretest
is 57.36. It was only 5% of students who achieved the standardized scores
(KKM). Then the mean of the students` scores in Post-test is 66.45 and there were
32 % of students who achieved the standardized scores (KKM). Then the mean of
the Post-test in cycle 2 is 79.72. All the students achieved the standardized scores
(KKM). Then from the observation, the students showed their good attitude
during teaching learning process. Besides that, the questionnaire also showed that
76% of students had positive perception towards diary writing. Accordance with
the result, it indicates that diary writing can improve the writing skills of the first
grade students of SMK Komputama Jeruklegi.