<p>The bruchid beetle <i>Acanthoscelides obtectus</i> is a major pest of stored legumes, and alternative control strategies are needed to reduce reliance on synthetic insecticides. This research evaluated the toxic, food preference, and behavioral effects of potassium soap on adult <i>A. obtectus</i> under laboratory conditions. Concentration–mortality data showed a good fit to the probit model, confirming the toxicity of potassium soap and estimating the median lethal concentration [LC₅₀ = 12.85 mL L⁻¹ (95% CI 9.25–20.65)]. Survival analysis over a 72-h exposure period revealed significant, concentration-dependent reductions in survival, declining from 99.9% in the control to 71.1%, 48.1%, 32.4%, and 9.51% at LC₂₅, LC₅₀, LC₇₅, and LC₉₀, respectively. Food preference assays indicated that bruchids significantly avoided treated bean grains at higher concentrations (LC₇₅ and LC₉₀), showed no preference at LC₅₀, and preferred treated grains at LC₂₅. Repellency tests corroborated these results, with potassium soap acting as an attractant at LC₂₅ and LC₅₀ but as a repellent at LC₇₅ and LC₉₀. Notably, these biphasic, concentration-dependent behavioral responses provide evidence of hormesis at sublethal exposures. Overall, potassium soap exhibited both lethal and concentration-dependent behavioral effects on <i>A. obtectus</i>, suggesting that it warrants further evaluation as a potential component of integrated pest management strategies for stored legumes.</p>