The eucalyptus plantations are experiencing considerable development in the world, but are also subject to controversy. The present study aimed to evaluate the floristic diversity and the allelopathic reflection of Eucalyptus saligna plantations in the Baleng forest reserve in Western Region of Cameroon. The experimental design consisted of five parcels, one control parcel and four parcels of Eucalyptus of different ages. In each of the five parcels, three plots of 9 m2 (3m x 3m) were randomly selected for the assessment of floristic diversity and soil sampling. In each plot, a circular section of 100 m deep hole was dug and soil samples were collected at three depths (20 cm, 50 cm and 100 cm). Soil analysis were made using the gravimetric method. It emerges from that study that the water content of soil decreases with the deep of soil and age of parcels. A total of 1593 individuals were recorded, grouped into 21 families and 55 species. The three most represented botanical families are Fabaceae (21%), Asteraceae (20%) and Poaceae (16%). But with regard to the number of individuals, the Poaceae family is the most represented with 36% of the individuals, followed by Asteraceae (21%) and Caryophyllaceae (11%). Herbaceous species are largely predominant (92% of individuals). There was no significant difference between the specific richness of the control plot and that of the eucalyptus plots at the 5% threshold (Turkey Test). Eucalyptus Saligna did not adversely affect the floristic composition of the understory vegetation.