The purpose of this study is to investigate pronunciation deviations of German diphthongs for Korean learners residing in Daegu and Gyeongbuk regions. When Korean learners utter German diphthongs such as /a͜i/, /a͜u/ and /ɔ͜y/, this study is to analyze what phonetic features appear to be realized in segmental and suprasegmental perspectives and find out the reasons to eventually contribute to reducing Korean learners’ pronunciation deviations of German diphthongs. The results of the experiment are as follows. First, when Korean learners utter German diphthongs, they were realized mostly in two syllables. Second, as to the descent degree of intensity in a suprasegmental perspective, the difference in a case of intensity realization of /a͜i/ between Korean learners and Germen speakers was shown to be the biggest. Third, in terms of length (utterance duration), the biggest difference with German speakers was shown to be found when Korean learners uttering /a͜u/. Fourth, in a segmental perspective, the pronunciation deviation of /ɔ͜y/ was found to be the biggest. The reasons that these pronunciation deviations appeared may include the negative transference phenomenon of mother tongue that worked on deviations the most, and other correlations with lack of awareness of phonetic rules about the relations of German grapheme‐phoneme rules, phonetic features of German diphthongs,—for instance, features including a single syllable utterance, and/or the feature of intensity descent of syllables when consecutively connected to non‐syllables.