Itoman, one of the varieties spoken in the southern part of Okinawa Island, exhibits several tone patterns. Although the tone patterns of Itoman were examined in previous studies (Nakasone ms., Hattori 1959, Oshiro 1963, and Hirayama et al. 1966), they ended at the descriptive level, and no phonological accounts for the surface tone patterns were provided. Focusing on the nominal tone patterns, this study provides both phonetic and phonological accounts of the tone patterns of Itoman. To account for the tone patterns both phonetically and phonologically, I collected audio data during three fieldwork trips to Okinawa. Based on the analysis of the data, I found the following tone patterns: (i) falling, (ii) plateau with fall in a ga-form, (iii) plateau, and (iv) concave. In the autosegmental framework, I propose ten rules and their subrules, which systematically explain the four tone patterns of both monomorphemic and polymorphemic nouns.