The natural prey of medium-sized juvenile (ca. 3 mm) crab spiders Xysticus marmoratus Thorell 1875 inhabiting Eryngium biebersteinianum plants was studied on the Absheron Peninsula, Azerbaijan. The percentage of specimens found feeding on prey was low (3.4%). Xysticus marmoratus is a polyphagous predator with representatives of four arthropod orders found in its diet. The primary food of X. marmoratus was ants (Formicidae), which accounted for 83.3% of the total number of prey. The length of prey killed by X. marmoratus ranged between 0.87–7.50 mm (mean 2.96 mm) and constituted from 28.5–300.0% (mean 96.9%) of the length of their captors. The most frequently captured size group of prey was 50–70% the length of the spiders.