The assessment of fungi and bacteria species in the Rhizosphere of Rivers State University Forest Arboretum. The experiment was laid in a completely randomized design (CRD). A composite soil sample of Moringa oleifera (Lam.) and Annona muricata (L.) of 0-35cm depth was collected using soil auger. The fungi and bacteria isolated and identified from the Rhizosphere of the Forest Arboretrum are Rhodotorula sp, (F.C. Harrison) Aspergillus niger (van Tieghem), Microsporum audouinii (Gruby), Sporotrichum pruinosum (J.C. Gilman and E.V. Abbot), Aspergillus versicolor (Budapest and Treaty). Though Aspergillus versicolor and Microsporium audouinii were absent in the soil of Annona muricata. However, the bacteria isolated from Moringa oleifera and Annona muricata are; Bacillus sp (Ehrenberg) and Micrococcus sp (Schroeter and Cohn). Generally, five (5) fungi and two (2) bacteria organisms were isolated, identified and classified into their different phylum, class and genera and cell morphology/microscopic characteristics. The result on the Simpson’s diversity index of fungi and bacteria found in the Rhizosphere of Moringa oleifera and Annona muricata tree stand indicate that there was no diversity of Fungi found in both Moringa oleifera and Annona muricata tree stand (SDI = 1). Similarly the Simpson’s diversity index value of bacteria population found in Moringa oleifera and Annona muricata tree stand (SDI=0.67) was more diverse when compared to the bacteria isolated from Annona muricata (SDI = 0.00). The soil microbial populations are indeed important factors for determining soil quality of the forest arboretum. Most micro-organisms isolated and identified are useful in nutrient recycling in this study. Therefore it is recommended that tree species of Moringa oleifera and Annona muricata promoted some good numbers of micro-organisms and the micro-organism found play an important role in soil food web in Rivers State University Arboretum. However, Bacillus based fertilizers could be applied to the soil to enhance the plant available for nutrients in the rhizosphere and help to control disease causing pathogenic microbes to induce pest defense systems.