This thesis is a study of the case system of Kafinoonoo. Its focus is on marking of core and peripheral arguments. In addition, genitive case marking and case in different constructions like NPs, pronominals and passive are also discussed. In core argument, arguments in A/S position and arguments in O position have been seen. According to the data by which this thesis is conducted; arguments in A/S position are not morphologically marked. In other words nominative case in Kafinoonoo is morphologically unmarked. This is the first study to show that proper names, morphologically marked nouns, simple derived names behave differently with respect to O marking. Some of them are optionally marked, some of them are obligatorily marked, and still others can occupy the O position by lengthening their final vowels and then optionally marked. In Kafinoonoo there is no consistent way of accusative marking. Proper names including personal names behave in two ways in O position. They can occupy the position either by lengthening their final vowel or they can be suffixed by -n without lengthening. Personal pronouns especially1SIG, 1PLU, 2SIG and 3distal pronouns behave similarly in O position. As in the proper names they can lengthen their final vowels and then they can be suffixed by - n. Unlike these 3proximal pronouns, marked plural nouns and derived nouns are obligatorily marked in O position by -n. Modified NPs in S/A position are not morphologically marked, whereas they can behave differently in O position. Pronominals are also not marked in A/S position but they too behave differently in O position. These can either lengthen their final vowels or they can be optionally marked by -n. Genitive in Kafinoonoo is marked in different ways. Simple juxtaposition can show the genitive case. In addition, ‘-tʃ’ can mark the genitive case in Kafinoonoo. There is still a phonologically conditioned variant of ‘-tʃ’ which also can mark the genitive in Kafinoonoo. This is ‘-dʒ’ which marks the genitive of noun that end in / m/ followed by vowel. These all are discussed in this thesis and finally the main findings are summarized.