Most of the studies on tropical forests vegetation have tended to focus on trees with a diameter at breast height (DBH) greater or equal to 10cm, and limited attention has been paid to understory. This study was conducted in Uluguru forests in Morogoro region, Tanzania, with an objective of describing the understory tree composition, diversity and natural regeneration of some threatened species in the seven surveyed forests. Sampling was done in the forests whereby classification of understory was done into three layers: seedling (individuals with height < 1m), small sapling (DBH ≤ 3 cm), and large sapling (3 < DBH < 10 cm) layers. Large saplings were sampled in 20m × 20m plots, while subplots of 5m ×5m and 2m ×2m were placed at the centre of each plot for sampling small saplings and seedlings, respectively. A total of 2119 seedlings, 1798 small saplings, and 2585 large saplings belonging 91, 102, and 104 species, respectively, were recorded. Fabaceae was the most speciosefamily in all the studied compartments, and had higher familial importance value (FIV). The seedling layer had higher tree density than the large and small sapling layers, but the large and small sapling layers were more diverse than the seedling layer (p < 0.05).The species richness in each forest was significantly higher in the understory than overstory layer (p < 0.034); and the pairing was strongly positively correlated (r = 096, p = 0.0003). The Sørensen coefficients of similarities between understory and overstory ranged between 0.53–0.77, and were higher within each forest than among them. All forests revealed to have good regeneration, though it is important to understand that some species unveiled poor or hampered regeneration pattern.In summary, the understory was observed to be speciose than overstory layer; it was dominated by family Fabaceae, and the natural regeneration of the forests were good, however, some species need due attention.DAAD/DUCE