The aims of this research were to find out: 1) the typicals of error made by
the students of using relative clauses, 2) the most and the less potential problem of
using relative clauses. This research belonged to a descriptive research. The data
was taken on 21st February 2014 at the tenth grade students of SMAN 1 Rawalo in
academic year 2013/2014. There were 50 respondents were chosen as the sample.
The data analysis was done quantitatively and qualitatively. After analyzing the
data, it showed that the type of errors mostly happened in using relative clauses
were substitution error (53.5%), misordering error (27.04%) and addition error
(19.7%). Substitution error was the most error which was made by the students in
relative clause with percentage 53.5%. It also revealed that the most potential
problem of using relative clauses was relative pronoun “whose”, the percentage
was 40.4%, and the less potential problem of using relative clauses was relative
pronoun “whom”, the percentage was 17.0%.