Abstract: Field experiment was conducted for two successive seasons during (2004/2005) at the Shalakan Experimental Station, Kalubia Governorate, Egypt, to study the effect of morphactin (CF125), indole-3-butyric acid and their interaction at the concentrations of 0.0, 25, 50 and 100 mg L-1 in every case, on vegetative growth characteristics, yield and yield components as well as some bio-chemical constituents of maize grains. Foliar application of morphactin or indole-3-butyric acid had significant effect in increasing plant height, number of leaves/plant, stem diameter, Leaf Area (LA), Leaf Area Index (LAI), Net Assimilation Rate (NAR), flag leaf area, specific leaf weight, total dry weight/plant, as well as photosynthetic pigments at different stages of growth as compared with those of the control. Moreover, morphactin at 25 mg L-1 and indole-3-butyric acid at 100 mg L-1 recorded the maximum responses in most growth parameters at the three physiological stages of growth. Yield and yield components, i.e., ear length, ear diameter, number of grains/row, number of rows/ear, 100 grains weight, grain yield/plant, grain yield/fed., harvest index and shelling percentage as well as crude protein, total carbohydrates and oil percentage were also significantly increased by the increase of morphactin and indole-3-butyric acid concentrations up to 100 mg L-1 in maize plants as compared to untreated plants and other treatments. Data suggest that indole-3-butyric acid, morphactin and their interaction play a significant role in determining total yield in maize plants and that increasing their concentrations up to 100 mg L-1 result in increase total grain yield/fed (46.70, 43.55%) and oil yield/fed (72.72, 63.63%) at 100 mg L-1 of indole-3-butyric acid and morphactin, respectively as compared to control. Generally, foliar application of maize plants cv., single cross 10 with morphactin and indole-3-butyric acid at 100 mg L-1 singly or together with 50 mg L-1 of morphactin were the most effective treatments to get better results in increasing growth characteristics, yield and its components in addition to some metabolic constituents of maize grains. The increase in growth processes associated with these treatments are the consequence of a number of effects on the major physiological processes of plant like photosynthesis.