Five quinoa (Chenopodium quinoa Willd.) genotypes; namely, KVL-SRA2, KVL-SRA3, Regalona, Q-37 and Q-52 were evaluated, under rainfed and irrigated conditions, for their allelopathic potential. Four concentrations of 1, 2, 4 and 8 g/100 ml of the aqueous extract of all plant parts were assessed for their effect on the germination and initial development of some weeds and crops. HPLC/DAD/MS analyses were conducted for genotypes with highly inhibitory effects to determine their contents of phenolic compounds and saponins. The estimated EC₅₀ revealed that the aqueous extracts from genotypes grown under rainfed conditions had higher allelopathic activity than those genotypes grown under irrigated conditions. The suppressive effect of the extracts increased when the concentration of quinoa extracts increased. The highest reduction effects were achieved from Q-52; followed by Regalona and KVL-SRA2. Nevertheless, Q-37 and KVL-SRA3 caused minor amounts of inhibition in the tested plant traits. The negative influence of quinoa extracts was higher on monocotyledon plant species than on dicotyledon plant species. The highly susceptible plants were Hordeum vulgare, Allium cepa and Phalaris minor as compared to other tested plants. However, Vicia faba and Chenopodium album were slightly more susceptible plants. Qualitative-quantitative analysis showed sixteen flavonoids and three hydroxicinnamic acids (p-coumaroil derivatives); in particular, kaempferol dirhamnosyl-pentoside is the principal compound in Q-52 (11.25 mg/kg), while quercetin rhamnosyl-glucoside is the principal compound in Regalona (9.67 mg/kg). In quinoa, nine different aglycones, monodesmosidic, and bidesmosidic triterpene saponins were reported; in particular, in this work, hederagenin (hed), phytolaccagenic acid (PA), AG487, AG533 and AG515 derivatives were identified. Quinoa also contains biologically active phytoecdysteroids. Based on the bioassay results and its suppresive effect against weeds and crops, quinoa is considered as a crop with allelopathic potential that may have a negative impact on the growth of neighboring plants in the field and can be utilized for non chemical weed management.