This paper aims to define the Kaya native words, Pyŏkdin~Sungsan, Pal, Ili and Maidinyi, appearing in Samkuksagi (A Chronicle of the Three Ancient Kingdoms) and in Samkukyusa (A Reminiscent History of the Three Ancient Kingdoms). The three words denote the geographical denominations concerning the surrounding seas during the Kaya Dynasty and consequently may be accepted as genuine Kaya words. Pyŏkdin is a geographical name which consists of two morphemes, i.e., pyŏk+din (+a morpheme boundary). If we take the morpheme pyŏk for a sound-loan, we can infer it to be pyŏr. On the other hand, if we take it for a meaning-loan, it will be pyŏr. Of the two pyŏr is thought to be more persuasive. Assuming that Pali is an inscription of a sound-loan word, it can be read as pyŏri. Since there was no aspirate quality in the ancient Korean consonant system, pal can be read as bal, a prototype of Pyŏri appearing in the native songs of Shilla in the later period. Accordingly, pyŏri and its one-syllabic form pyŏl resulted from the omission of the suffix-vowel i which had coexisted. The back morpheme din as a meaning-loan may also be read as tal. The Kaya word meaning mountain was tal and so it is different from the word moe, which may be quite enough as to draw the attention to the subject at hand. Finally, assuming that Ili is a sound-loan, it can be read as Iri. It was the Kaya word relative to ting sung(star). And if one was to take the word Maidin as a sound-loan, it may be subsequently defined as a compound word of mai and din. The word mai appeared and was frequently used as an name of the places in the middle part of the ancient Korean peninsula. It implies mul(water) while din meant tal as noted above. Among the vocabularies pyŏri:iri, moe:tal, and mul:mai which coexisted in the Kaya language, pyŏri, moe, and mul may have been the native words of Kaya, and iri, tal, and mai may have been loaned from the words of Baekje. This active interaction of words bears witnesses that there had been vigorous cultural exchanges between the two nations.