Plants may favorably or adversely affect other plants through allelochemicals, which may be released directly or indirectly from live or dead plants (including microorganisms). The objective of this study was to examine the allelopathic effects of leaf leachates of Acacia nilotica and Eucalyptus rostrata on morphological, biochemical and molecular criteria of Zea mays L. (maize) and Phaseolus vulgaris L. (kidney bean). Concerning the seedling, seedling emergence was reduced with treatment with Acacia and Eucalyptus leaf leachates and growth parameters were generally reduced in both maize and kidney-bean. With respect to the internal metabolites, a gradual increase in the ABA concentration, decrease in the chlorophyll content and consequently the soluble sugars content is proportional to the increase in the concentration of the leaf leachates. Total DNA and RNA contents are highly significant increased in all treated samples of maize with respect to the control. On the other hand, kidney-bean samples showed mostly a significant reduction. Maize samples treated with Acacia show a highly significant increase in the level of soluble proteins while samples treated with Eucalyptus show a highly significant decrease. However, there is a highly significant decrease in soluble protein contents in Kidney-bean samples treated with both Acacia and Eucalyptus. With respect to the protein pattern, the allelopathic effect of both Acacia and Eucalyptus induced the formation of stress proteins. High and mid molecular weight proteins 244, 187, 143, 51.8, 41, 40.6 and 29.7 kDa were newly synthesized in response to the allelopathic effect of Acacia. On the other hand, mid and low molecular weight polypeptides 121.8, 116, 62, 52.9, 46.8, 45 and 40.6 kDa were recorded in response to the allelopathic effect of Eucalyptus. In maize treated with both Acacia and Eucalyptus, the 55.4 kDa protein was disappeared, while the proteins 40.5, 30.5, 29.7 and 26.5 kDa were newly synthesized. Moreover, in maize seedlings treated with Eucalyptus, the proteins 50.8, 41, 30.5, 26.8 and 26.5 kDa were recorded. The number of de novo synthesized proteins (chaperones) in maize samples treated with both Acacia and Eucalyptus (12-induced proteins; 121.8, 60.9, 55, 52.9, 50.8, 46.8, 41, 50.6, 30.5, 29.7, 26.8 and 26.5 kDa) were more than that induced in kidney-bean (10-stress induced proteins; 244, 187, 143, 116, 93.7, 51.8, 45, 41, 40.6 and 27.4 kDa). The genomic DNA of each treatment was subjected to four restriction enzymes (BamHI, EcoRI, HinfI and SamI). The resulting cleavage fragments had apparent low molecular sizes and appear as smears of digests whatever the concentrations of templates of DNA or restriction enzymes and the time of electrophoretic run. The highest degree cleavage was observed EcoRI. All studied samples showed different DNA fingerprints. All samples had on average 20-30% of their bands in common. The variability was higher in the bands in the region of the gel above 2.7 kb than in the bands below it. On the average, 50"5 bands were seen above 500 bp, ranging from 700 to 2400 bp. A clear information data was obtained using HinfI (5-base cutter) as compared to other enzymes (6-base cutter) which may indicates the presence of stimulator which facilitate the recognition of the nucleotide sequence which is specific for each enzyme and the cutting site inside it. This indicates that the percentage of shared bands in DNA fingerprints of maize and kidney-bean might be used as a measure of genetic difference and demonstrate that the restriction site mutation assay can detect mutations. Present results indicate that, Eucalyptus is more effective in affecting morphological, biochemical and molecular criteria and that the monocot plant (maize) is more tolerant than the dicot one (kidney-bean). We can suggest that the allelopathic chemicals of both Acacia and Eucalyptus may have the potential as either biological herbicides or templates for new herbicide classes (i.e. biological control).