A.seyal trees are widely spread species in Sudan, that could be recommended as agro forestry species but before that the existence of inhibitors must be examine . so this study was conducted in order to investigate the effect of tree age and the distance from the tree crown on the germination and mortality of sorghum. four categories diameter at breast height as indictor of the trees age selected (32-51cm, 52 -71cm, 72-81 cm and 82 –above cm) and Five trees in each category and two sorghum varieties (Tabat and HSD) were grown underneath these trees in different distance after the crown (1, 2 and 3 meter) The germination percentage, seedling mortality were recorded. The results showed that the oldest trees have significantly decreased the germination percentage even when the sorghum (Tabat variety) was grown 3 meter far from the crown (table 1).  But when this experiment was repeated with anther variety (HSD) the results were little bit varied . the seedling grown underneath the oldest trees(91- ≤ cm) had the lowest mortality percentage for both varieties and three distance from the tree crown (1,2 and 3 m). This results suggest that the different varieties have different response to inhibitors released by A. seyal trees.