The present paper is an experimental study that addresses the insertion of the palatal glide [j] and glottal consonants [h] and [?] to prevent vowel hiatus in Persian. Data included Persian words involving the sound sequence V1-V2 where V1 was the last sound of the root and V2 was the beginning vowel of a suffix (either derivational, inflectional or enclitic). In the previous literature it has been assumed that the insertion of a consonant in VI-V2 sequences in Persian is sensitive to the phonetic specification of the first vowel. Thus, words were selected such that V1 was any of the six vowels of the Persian sound system. Acoustic analyses of the data included measurement of variation of the first and second formant frequencies as wells as variation of energy in the FFT spectra (overall intensity and intensity in the higher frequency bands). Results suggested that while the insertion of [j] changes the frequency of the first two formants F1 and F2, the insertion of the glottal consonants fails to trigger frequency changes in the spectra. The results further suggested that the intensity of higher formant frequencies is more highly to reduce due to the insertion of mediating consonants than overall intensity or the intensity of lower formant frequencies. The results were interpreted to suggest that variation in phonation type is the most noticeable acoustic change that occurs when the glide [j] or the glottal consonants [h] and [?] is inserted in V-V. This change is the least phonetic change that is required to reform vowel hiatus in Persian by turning the ungrammatical sequence V-V to the grammatical VCV one. From the phonological point of view, the findings presented in this research are in line with Chomsky and Halle's (1968) model of phonetic features in which glides and glottal consonants are represented by the same features [-vocalic] and [-cons].