Many research studies have been done in the Mungo-River valley, they were mostly concerning the genesis and stratification of outcrops, but not really their petrology (description and classification). According to those reasons, this article is going to increase the petrology’s understanding of Mungo-River’s cretaceous outcrops, in Douala sub-basin. So, the studies have been done on Moundeck village’s outcrops and near the railway bridge on the Mungo-River. In fact, the studies were concerning the description of eight outcrops; the classification of their facies and the interpretation of their genesis. The description of outcrops has showed that they are constituted of positive and negative sequences. The thin sections have permitted to classify the facies described as litharenites and lithic arkoses, which are friable rocks. The genesis of Mungo-River’s outcrops could be understood according to two approaches. On the one hand, the sedimentary structures such as intercrossed and oblique stratifications observed on outcrops signify that, the sedimentation had been taken place in a fluvio-deltaic environment. On the other hand, the positive and negative sequences delimited on described outcrops, testify the influence of sedimentary cycles (transgression and regression) within the depositing environment.