The growing demand for sustainable and cost-effective alternatives to synthetic nematicides has driven interest in naturally derived compounds with selective activity against plant-parasitic nematodes. In this study, we evaluated the bionematicidal potential of undecanoic acid, a naturally occurring medium-chain (C11) fatty acid, against two economically important root-knot nematodes: Meloidogyne ethiopica and M. graminicola. Direct contact bioassays demonstrated 100% mortality of both species within 24 hours of exposure to a 1 mg/mL concentration, confirming strong and rapid nematicidal activity. In contrast, exposure of a non-target, the free-living soil nematode Cephalobus sp., resulted in only ca. 40% mortality, suggesting a favorable degree of selectivity toward phytoparasites. Additionally, environmental fate modeling indicated a predicted distribution of this compound of ca. 62 % in soil, 20 % in air, and 16 % in water environmental compartments, consistent with its use as a soil-applied agent, while highlighting the need for environmental risk assessment under field conditions. As a naturally sourced compound, undecanoic acid offers advantages over synthetic nematicides, not only due to its biodegradability and potential reduced environmental impact, but also its lower cost compared to commercial pesticide active ingredients. The selective toxicity of undecanoic acid makes it a favorable candidate for integrated pest management (IPM) programs, particularly in low-input or organic systems. These results underscore the potential of this naturally occurring fatty acid as an effective and sustainable tool for nematode control. Further studies on formulation optimization, persistence, and field efficacy will be needed to fully realize its application in agricultural systems.