In traditional phonology, the feature of [voiced] is one of the main descriptive aspects of sounds in classifying the underlying opposition, and the feature of [aspirated] is not contrastive because it is predictable. On the basis of Laryngeal Phonology, [voiced] is not contrastive for all classes of phonemes in all languages of the world. Contrast lies in the stability of the phonetic cues for marked segments as opposed to the unmarked ones. Because of the instability of voicing in initial position of (stressed) syllables in the obstruents of some languages, it cannot be considered as a contrastive feature. Under this view, aspiration is contrastive because it is stable in those positions of the syllables. This paper aims at describing Persian phonemes in the framework of Laryngeal Phonology, proposed by Idsardi and Avery (2001). The results show that the laryngeal contrast in Persian obstruents, like English, is of the Ø -GW type, i.e., one which marks obstruent consonants with the laryngeal dimension of [glottal width], completed with [spread] gesture. On the basis of the evidence provided, it is claimed that Persian is an aspiration language and voicing is contextually determined rather than contrastive. On the contrary, voicing is contrastive for sonorant consonants and underlyingly determined which finally completed with [glottal tension] dimension.