Assimilation is a phonological process in which a sound becomes more like its neighboring sound. This process can occur either within a word or in between words and is of two types depending upon its directionality –regressive or progressive. Maring exhibits total contact regressive assimilation within word boundary. This is a prevalent morphophonological phenomenon that affects the formation of perfect aspect - kur and genitive case marker - jəi. For instance, if a verb ends with -ŋ the perfect aspect will become - ŋur, if it ends with -l then the perfect aspect will become - lur and so on. The same process is applicable with the genitive case marker - jəi. If the noun, i.e. the possessor ends with -m or -n or -r then -jəi will become -məi, -nəi and -rəi respectively. These changes occur in reference to all the verbs and nouns (the possessors). The target sounds change completely in reference to its preceding segment for facilitating a smooth, effortless and economical task of utterance. This paper will discuss in detail the cause of the assimilation, the rules and constrains, and the various implication the process has on the language, the speakers and second language learner.