Allelopathy involves the biochemical interactions among plants and other species, through the release into the environment of chemical compounds named allelochemicals.  Medicinal plants and vegetable wastes are a primary and neglected source of secondary metabolites which can play a role as allelochemicals . This review deals with the assessment of allelochemicals  from Ruta graveolens and Olive oil waste waters as potential natural pesticides in sustainable agricultural systems. Using chromatographic and spectroscopic methods, a bioassay-oriented  study of rue and  olive oil waste waters allowed us isolate and identify, some allelochemicals, such as coumarins, flavonoids, terpenoid derivates phenylpropanoids and polyphenols. Successively, a  rue infusion, some chromatographic fractions and pure isolated compounds were assayed in vitro and in vivo for compounds for their biological activities on seed germination and radicle growth, algae, fungi and insects. Microscopic observations on cellular effects of allelochemicals in target organisms were also performed. Some allelochemicals (e.g. 5-methoxypsoralen) severely inhibited the growth and development of tested organisms. Results suggest that rue and olive oil waste waters are a cheap source of allelochemicals whose exploitation as a natural pesticides deserve attention. Eco-toxicological studies are in progress.