The nutritional quality of Persian clover (Trifolium resupinatum), an important pasture crop, depends not only on a high protein content but also on the occurrence of animal health and welfare promoting phytochemicals. Nine phenolic constituents present in the aerial parts of this species were isolated and their structures confirmed by NMR and ESI-MS analyses. The compounds included two chlorogenic acids, four quercetin and two kaempferol glycosides, as well as the isoflavone formononetin-7-glucoside. The concentration of isoflavone was low, not exceeding 1.2 mg/g of dry matter. The concentration of flavonols ranged between 5.9 and 11.8 mg/g, depending on the sampling dates, with the highest concentration occurring in the first cut. A similar trend in the concentration was found for chlorogenic acids, which ranged from 2 mg/g in summer to 7.3 mg/g in spring.