This paper describes the use of graphene oxide/silica modified with nitro-substituted tris(indolyl)methane as a solid-phase extraction sorbent for the determination of organic acids. The resultant graphene oxide/silica modified with nitro-substituted tris(indolyl)methane was characterized by FTIR spectroscopy and adsorption experiments. Solid-phase extraction parameters such as sorbent type, sample solution pH, sample loading rate, eluent salt concentration, eluent methanol concentration, elution rate, sample loading, and elution volume were optimized. The method showed good precision, accuracy, sensitivity, and linear response for organic acids analysis over a concentration range of 1–100 μg/L for benzoic acid, p-methoxybenzoic acid, and salicylic acid and 5–100 μg/L for the remaining organic acids (cinnamic acid, p-chlorobenzoic acid, and p-bromobenzoic acid) with coefficients of determination (r²) of higher than 0.9957. Limits of detection from 0.50 to 1.0 μg/L for six organic acids were achieved. The developed method was successfully applied to determine organic acids in real samples.