The study entitled Phonological Acquisition in Children 4-5 Years of TK Kartika III-30 Infantry Battalion (Yonif) 405 Surya Kusuma Wangon Sub-District, Banyumas Regency aimed to illustrate the language acquisition in the phonological field and its obstacles to children 4-5 years at TK Kartika III-30 Yonif 405 SK. This research method covered the research type, data and data sources, as well as research methods and techniques. The research type was a qualitative descriptive. The data obtained in this study was the vocabulary of children 4-5 years at TK Kartika III-30 Yonif 405 SK. The data source was the utterance of children 4-5 years at TK Kartika III-30 Yonif 405 SK. The research implemented three stages: (1) data provision, (2) data analysis, and (3) result presentation. At the stage of data provision, the basic method was tapping, then advanced techniques were uninvolved conversation observation, record, and note-taking techniques. At the stage of data analysis, it implemented distribution method and shared technique (BUL). Determining instrument was part of the language itself, whereas the referential identity method was with dividing key-factors technique (PUP). The instrument used was the children utterance obtained during the study and the sorting used in this study was speech organs or phonetic articulatory organs. At the stage of result presentation, the data was analyzed through informal and formal methods, namely common words and formulation of sign or symbol. The research results discovered phonological
acquisition in the form of vowels, diphthongs, consonants, clusters, phoneme distribution, and its obstruction. These obstructions originated from the children, parents or family, and environment. The most common difficulties experienced by children were acquiring consonants. Difficulties in vocal acquisition were dominated by acquiring vocal [e] and [∂], diphthong was dominated by acquiring [ai], consonant was dominated by acquisition [r], and cluster was difficulties in [dr-] and [kl-]. It was due to the children with problems of language mastery. In the phoneme distribution, it was discovered several vowels and consonants which could not be uttered completely. For example, vowel [∂] can only be uttered the starting and middle position, whereas the consonants of [w], [j], [c], and [g] cannot be uttered in the final position.