Diphthongs are double vowel sounds made by combining two vowels in the same syllable. During their articulation in the oral cavity, the first vowel sound glides onto the next vowel from one position of the mouth to another within the same syllable. That's why they are heard as single-vowel phonemes by listeners. Because of a gliding movement in their articulation, most learners find them difficult to articulate and understand them at first. Hence, they can be tricky sounds to master for non-native speakers. The aim of this research is to explore the perceptibility of North American English diphthongs (NAE), which are /a[near-close back rounded vowel], o[near-close back rounded vowel], e[near-close near-front unrounded vowel], [open-mid back rounded vowel][near-close near-front unrounded vowel], a[near-close near-front unrounded vowel]/ by Turkish English language teachers. A pre-test will be used to measure the perception of them in vocabulary items, which will be given to 30 Turkish English language teachers in a five scale multiple choice tests. The participants will be asked to choose the correct option. Then, a three-hour implicit and explicit teaching will be conducted by doing practices in a variety of exercises in the classroom. After the elapse of two weeks, the same pre-test will be administrated to the participants as a post-test. A comparison and contrast of the two tests results will be made to find out the existence and degrees of the perceptibility of the diphthongs in vocabulary items by Turkish English language teachers.