Harsusi is one of the five Modern South Arabian (MSA) languages spoken in the Sultanate of Oman. It is one of the least studied and known about languages in this group of Semitic languages. It is considered as a shifting language by the Ethnologue (Simons, G. F. & Charles, D. F., 2018) with around 6000 speakers. Being spoken in the desert, in the middle of Oman, Harsusi enjoyed a relative isolation for some time from the other surrounding languages including Arabic; however, after 1970 Harsusi became into direct contact with Arabic. This direct contact, in addition to not being systematically taught and learned in official contexts, pose threats at the situation of Harsusi in Oman. Moreover, there is a scarcity of thorough linguistic studies on Harsusi and such studies can help in both preserving Harsusi, and understanding the features of the (MSA) group as a whole. This report will provide an overview of the (MSA) language group. It will investigate the phonological structure of Harsusi in detail and provide a descriptive analysis of it. The main goal of this report is to explore the distribution of the sounds in Harsusi. It will explore the phonemic realizations in addition to the allophonic variations and the rules governing their occurrence in different environments. Moreover, it will look at the syllable structure and the stress patterns in Harsusi. Understanding the phonological structure of Harsusi is very important for any future studies on the morphology, syntax or semantics of Harsusi