Allelopathy phenomenon involves secondary metabolites produced by plants, algae, bacteria, and fungi that influence the development of biological systems. It´s seen as an ecological alternative to the use of biocides due to low damage to the environment. Previous studies showed that Solanum palinacanthum Dunal (Solanaceae) leaves contain allelochemicals able to inhibit the growth of Sesame and development of phytopathogenic fungi. This work searches for allelochemicals in fruits of S. palinacanthum. Fruits were stored at 50^oC for dryness and grounded to obtain a powder. A crude extract(CE) was made by mixing the powder with distilled water in concentrations 1%, 2%, 3%, 4% and 5%(w/v). A polarity gradient made of petroleum ether, dichloromethane, methanol and water, in this order, was used to obtain fractionated extracts. Twenty grams of powder were mixed with 100mL of each solvent to extract compounds with different polarities. The solvents were evaporated and petroleum ether and dichloromethane extracts were discarded (not water soluble). Methanolic and aqueous compounds were dissolved in water to form methanolic(ME) and aqueous extracts(AE) in the same concentrations used for CE (1%-5% w/v). Brachiaria decumbens Stapf (Poaceae) was used as receptor species. For germination test, twenty seeds were placed in Petry dishes with a Whatman #1 paper filter imbibided by 6mL of CE, ME or AE, at concentrations described, for seven days. In growth experiment, B. decumbens seeds were germinated in water and placed in gerboxes having a Whatman #1 paper filter imbibided by 12mL of extracts, at same concentrations, during six days. All experiments were made in triplicates, in a B.O.D. chamber at 25^oC, with 12hr photoperiod. Water was the control treatment. No extract affected germination of B. decumbens, nevertheless, CE, ME and AE inhibits shoots and root growth. Shoot growth inhibition for CE, at the highest concentration (5%), was 47% compared to the control. Root growth inhibition was 84%. Fractionated extract (ME and AE) showed reduced toxicity to B. decumbens when compared to CE. ME inhibition was 21% to shoot and 59% to root growth, in relation to water. AE inhibits 12% of shoot and 76% of root growth. Results show that S. palinacanthum fruits are allelopathic to B. decumbens and that additive or synergic effect may be acting in the phenomenon, since a mixture of compounds results in a stronger inhibition.