Allelopathic compounds as naturally occurring herbicide have originally reported from local vegetation since B.C. 300. These compounds are known as secondary plant metabolites which released from plants into the environment often attract or repel, nourish or poison other organisms. In recent, many natural plant allelochemicals be used to attempt to biologically or ecologically control weed among worldwide weed scientists. Some allelochemicals have also used as fungicides, insecticides, and nematodicides, and were less than man-made agrochemicals to damage the global ecosystem. It makes efficient use of resources internal to the farm, relies on a minimum of purchased inputs. Some scientists selected for allelopathic activity when breeding weed-controlling cultivars of rice, sorghum, cucumber, surflower etc. Thus, this paper is focused on allelopathic compounds isolated from cultivated crop with the high potential of prospective herbicides. The most environmentally acceptable and sustainable approach to utilization of allelopathy for weed control is to develop plant cultivars with proven allelopathic characteristics. In rice accessions, there are 60 cultivars/lines which have known as allelopathic activity and some of these cultivars control weed more less 90% within certain radius of activity. These accessions are originated from 15 countries including Korea, Japan, USA, India, Philippines, Indonesia, Laos, Taiwan, Afghanistan, Mali, Pakistan, Colombia, Egypt, China, and Dom. Rep. From these cultivars, the most common allelopathic compounds identified in rice are p-Hydroxybenzoic, Vanillic, p-Coumaric, and Ferulic acids. In addition, allelopathic lines of the following crop have shown inhibition of weed growth : beet (Beta vulgaris), lupin(Lupinus spp.), com(Zea mays), Wheat(Triticum aestivum), oats(Avena spp.) peas(Pisum sativum), barley(Hordeum vulgare), rye(Secale cereale), and cucumber(Cucumis sativus). Thus, future allelopathy research must be designed its potentially phytotoxic propertices and the ecotoxic features of the allelochemicals from release to degradation ; its ecological sustainability, its allelopathic effect in early growth. stages, and selectivity properties in combination with chemical stages, and selectivity properties in combination with chemical concentrations. Also, research approach in allelopathy might be screened for highly allelopathic germplasm collection of crops, the idea being to ultimately transfer this agronomic character into improved cultivars by either conventional breeding or other genetic transfer techniques.