Organic agriculture has become a major dialog considering the negative impacts of agrochemicals. Application of herbal extracts have been studies, however, the results are not very promising. The inter-reactions of various chemicals in crude extracts, relative concentrations and volatalities of of active chemicals, etc.  may be the resons. Based on the similar studies on Eucalyptus leaf extracts found to be effective agaist a range of weeds however, there were no studies to understand the active chemicals. Eucalyptus is of ample availability in the country and alsoreported to have negative impact on the biodiversity where the populations are present. Therefore, studying the herbicidal activity would be beneficial in both biodiversity conservation and as a herbicide suitable for organic farming. Crude aqueous extracts (200 g of leaf powder extracted to 1 l of water at 70OC diluted to 8 l) were tested against the weeds in rice cultivation to re-evaluate its herbicidal activity and other benefits. The results show that the extracts are effective in management of weeds at 4 days after broadcasting. The crude extracts were analysed for the constituents using HPLC followed by LC/MS and GC/MS. Out of the total  of 32 detectable constituents recorded 17 were previously recorded to have herbicide activity. Results of the current study will be used in isolation of identified active compounds with herbicide activity and conducting small scale evaluation trials for validation of results followed by large scale researcher managed field trials. The treatments will be consisted of single chemical trials and possible combinations of the chemials after careful understanding of their chemical inter-reactions. Finally it is expected to develop a novel commercial biobased herbicide which is ecologically friendly and suitable for effective weed management in rice.