Chemical analysis of aqueous extract of Ziziphus mucronata Willd. was determined by liquid chromatography–mass spectrometry (LC-MS) analysis. Among the 11 compounds found, catechin, rutin (quercetin 3-O-rutinoside), delphinidin-3-glucoside, isoquercetin (hyperoside) and quercitrin (quercetine3,7-O-L-dirhanmopyranoside) were identified as the major phenolics components in this aqueous plant extract. To elute the target compounds, the fractionation of crude extract was carried out on solid phase extraction (SPE) columns. The different fractions (from FZ1 to FZ5) obtained after fractionation were evaluated in vitro against economically important foliar fungal pathogens of peanut, including Cercospora arachidicola, Phaeoisariopsis personata and Puccinia arachidis. The treatments with Z. mucronata fractions were compared with negative control (water) and standard solutions of cathechin and rutin (1 mg/mL). All the fractions recorded an inhibitory effect, firstly on conidial germination and germ tube elongation, secondly on disease evolution on peanut leaves previously inoculated by fungi; the level of efficiency of inhibition varied from 40.55 (FZ1 against C. arachidicola) to 57.14% (FZ2 and FZ3 against P. arachidis). Then, spores of P. arachidis seemed to be more sensitive to the treatment.