The extracts of P. deltoides and U. wallichiana were tested for their allelopathic effect on biochemical constituents of Zea mays L. (Maize), Phaseolus vulgaris L. (Kidney bean) and Helianthus annus L. (Sunflower). The findings revealed that total chlorophyll, total soluble sugars and soluble proteins were reduced in the recipient species by all the extracts used. The chromatographic investigations revealed that the secondary metabolites identified in P. deltoides were dominated by phenolic glycosides and few phenolics and those identified in the extracts of U. wallichiana belong to the group of aliphatic hydrocarbons and triterpenes. Maximum number of allelochemicals were recovered in extracts obtained after 24 hrs long soaking time. Prolongation of soaking time beyond 48 hrs did not yield any component from the extracts of both the species. The compounds identified in both the species under investigation are known to induce inhibition in plant growth and development and hence their direct exposure could lead to reduction in overall productivity.