Quinoa (Chenopodium quinoa Willd.) is a grain crop grown primarily for its edible seeds. The plant has originated in the Andean region of South America, where it was domesticated 3,000-4,000 years ago for human consumption. Because quinoa has a high nutritive value and desirable agricultural traits as tolerance to drought and salinity, it has gained increased demand in recent years. The winter climate in Egypt favors good production of quinoa and it has already been cultivated in saline soils in Upper Egypt. More, recently in 2014, downy mildew was recognized in plants of two Egyptian quinoa trials at Giza and Ismaeliya governorates. Infected plants showed small to large irregular chlorotic lesions with grey mildew on leaves (Fig.1), often leading to early leaf defoliation. Light microscopy revealed presence of colorless dichotomously branched sporangiophores (2-3.2μ width), slightly curved at the far point bearing hyaline sporangia (Fig.2). Spores are deciduous, mostly ovoid, 11.0- 15.6μ x 20.0-25.5μ (Fig.2). Dark brownish oospores were observed embedded into leaf tissues. The disease is caused by Peronospora variabilis Gäum, formerly Peronospora farinosa f.sp. chenopodii Byford, (Choi et al., 2010). It is expected that this disease could be a potential constraint for quinoa production in Egypt. To minimize the effect of downy mildew on the seed yield, in depth studies are to be done to develop control measures and accumulate information about disease parameters under local conditions.