The aim of this research was to describe the students‟ errors in pronouncing English diphthong of the
sixth semester of Muhammadiyah University of Purwokerto in academic year of 2015/2016. The type of
this research was descriptive research. The population of the research was 106 students and 21% of them
(20 students) used as sample of this research. The instrument used was a test, using 80 words (used in
teaching and learning process). In analyzing the data, error analysis was used in which there were four
steps: transcribing the students‟ pronunciation into the phonetic transcriptions, grouping the students‟
errors in pronouncing English diphthongs into separate divisions, employing the percentage descriptive
analysis to count all error and interpreting the result of the data analysis. The result of the analysis showed
that students made 52% errors in pronouncing English diphthong. The errors were 27 % on centering
diphthong and 73 % on closing diphthong. There werethree dominant errors on English diphthongs : [ʊə],
[əʊ], and [eɪ]. The factors causing students errors are students‟ mother tongue and word orthographic
writing form.