This thesis has attempted to investigate and describe the word formation processes inrnDiddessa Mao, the variety of Northern Mao of Omotic family spoken around DiddessarnRiver Valley. Derivation, compounding and reduplication have been dealt with as thernmajor word formation processes. The derivational processes in this variety of Maornincluded nominalization, verbalization, and adjectivalization.rnDerived nominals such as: manner nominals suffix /-Ã¤/ to action verbs. Abstractrnnominals suffix/-iyÃ¤/ to adjectival and nominal bases. Action nominals suffix /-i/ tornverb roots, and result nominals suffix /-e/ to verb bases. In verb derivation causativesrnare derived from verb roots, adjectivals and nominal bases by suffixing /-sisa/.rnPassives suffix /-ekâ€™-/ to transitive verb roots. Reflexives suffix /-inke/to simple verbrnroots, causative verbal stems and intensive verbal stems. Statives attach thernmorpheme /-inke/ to adjectives. The reflexive /-inke/ is homophones with the stativern/-inke/. Adjectivals are derived from nominals by suffixing the morpheme /-itÃ¤/.rnCompounding in this variety of Mao is formed through the combination of two or morernwords from the same or different word-classes. Compound nominals are formed fromrnverbals and nominals or from two nominals. Compound adjectives are formed fromrntwo adjectivals, or nominals and adjectivals, adjectives and nominals and number withrnnominals. Compound adpositions are formed from two adpositions.rnIntensive verbal stems are formed from verb roots through complete reduplicationrnprocess. Adverbials are derived from nouns that refer to time with the suffix /-at/.rnSome phonological, morphological, syntactic and semantic characters of thernderivatives and compounds are considered in this study. For all kinds of wordrnformation processes, word formation rules (WFRs) have been proposed and theirrnpositions are also described.