Legume–grass mixtures showed a weaker response to adverse environmental conditions than to monocultures. A yield decrease due to the scarcity of water is well documented, while the impact on the food value is inconsistent. Therefore, we undertook studies to assess the impact of water deficit in the soil on the content of the nutrients in alfalfa and Festulolium grown in monoculture and in mixture. A pot experiment was carried out in 2012–2014 in a completely randomized design, with four replications. The research was carried out at two levels of soil moisture: 70% field water capacity FWC (optimal conditions) and 40% FWC (drought stress). We found that the effect of drought stress on the food value of alfalfa and Festulolium was smaller than on the yield. Water deficit caused a significant yield decrease, the biggest in alfalfa in monoculture. Drought stress significantly reduced the content of crude fibre, the contents of crude protein and crude fat tended to increase. The influence of stress on water‐soluble carbohydrates content was not determined. Nutrient content was varied depending on a species. Introducing alfalfa as a component to a mixture with Festulolium caused a significant yield increase and improved the nutritional value of dry matter.