This paper analyzes segmental decomposition processes in interlanguage mapping, showing that the major place property is the most important factor among all phonological properties to be preserved. For instance, the duality of the Japanese fricative /ɸ/ triggers segmental decomposition both in Japanese loan adaptation of the English /f/ and in Korean adaptation of the Japanese fricative. Moreover, the targets of decomposition may include affricates, fricatives, and even a velar nasal. Furthermore, allophonic variation in the source language may show up in the recipient language as variations, even in transcription. Finally, I discuss the role of VOT which contributes to the interlanguage mapping.