For many years, researchers on phonetics have been trying to characterise a sound of languages from various points of view and employing a variety of approaches and methods. Some researchers have focused on finding some common features across languages while others have concentrated on the phonetic details of a particular language. This thesis aims to investigate, using acoustic analysis methods, the properties of non-identical vowel sequences of a particular language, Japanese, thereby enhancing our knowledge of the phonetic characteristics of this particular language and in the process shedding light on phonetic categories which are routinely used across languages.