Due to globalwarming, a permanent rainfall deficit and higher temperatures reduce the available water in the soil, which severely influences plant water status. Current research needs to address ways to overcome these problems in order to maintain crop yield. The beneficial effects of seaweed extracts against abiotic and biotic stress factors of plant growth is well known but the use of microalgae for the same purpose is not well described. The aim of the present work wass to investigate the plant biostimulating effects of the cyanobacterium Nostoc piscinale on the winter wheat variety "Bőség". Experiments were carried out over three years in Hungary at the Mosonmagyaróvár Faculty Farm. Freeze-dried cyanobacterium was re-suspended in water (0.3 or 1.0 g/l.) and sprayed at 400 L/haon wheat leaves at tillering and ear emergence. Root weight, relative water content (RWC), chlorophyll and proline content of leaves were measured during the vegetation period. Ear number, ear length, grain numbers in ear, thousand grain weight and yield were measuredat harvest. The most economic and highest yield increase was obtained by 0.3 g/l. treatment with N. piscinale at tillering and ear emergence. Beneficial effects included a stronger root system, elevated leaf RWC, higher proline content and increased leaf chlorophyll content, which remained high in plant leaves treated with N. piscinale for one or two weeks longer than in the control leaves. The high chlorophyll content extended the productive vegetation period of the treated plants. Cyanobacterium treatment increased the ear number, ear length, grain number per ear, thousand grain weight and yield of the wheat crop.