The field experiment was studied at IIHR Hessaraghatta during rainy season of 2001-02 to study the allelopathic potential of neem extract in horticultural crops.The experimental plots were laid out with randomized block design using three replications and seven treatments with different combinations including herbicides and bio-herbicides of neem, mango, eucalyptus, guava, and sapota. The efficacy and inhibition effect of neem extract was found significant @ 1 kg/sq. Mt. of bed without affecting microflora and physico-chemical properties of soil and reduce the dependence on chemicals in crop production to certain extend so as to get maximum economic yield. The neem material studied for biochemical investigation using HPLC Schmdz classVP with C-18 column and mobile phase of flow rate 1min /ml, meoH: AcoH: H2O (HPLC grade) of 5:20:75 bi-gradient elution. The maximum intensity of the peaks were found and drawn their standard curves and recorded at 40 min, 50 min and 62 min. The parent compounds were detected i.e para–benzoic acid, catechuic acid and caffeic acid respectively. These compounds were substantially to reduce the growth of temporary and permanent weeds at certain extent without affecting the plant system for long term horticultural crops.