The results of research carried out in 2005-2007 in Experimental Station in Osiny were presented in the paper. The aim of the study was comparison of yielding of several winter wheat varieties cultivated in organic and conventional crop production systems and evaluation of the reasons of yield differentiation in these systems. The analysis contained: the yield of the grain and the elements of their structure, the evaluation of infestation by stem base and leaves fungal pathogens, quantitative and qualitative analysis of weed infestation, the total protein content in the grain. In organic system the yield was 20% smaller than in conventional one taking in account mean for four varieties during 3 years. In organic system Zyta reached the biggest yield but Sukces and mixture of variety the lowest one, whereas in conventional system Kobra yielded the highest and Roma the lowest. The old varieties (Ostka Kazimierska, Kujawianka Więcławicka, Wysokolitewka Sztywnosłoma) were not very useful for cultivation in organic system. The weed infestation in winter wheat cultivated in organic system depended more on density of the crop canopy than morphological features of varieties. In organic system stem base diseases were unimportant, contrary to leaves diseases. The winter wheat grain from organic system contained low level of total protein than from conventional one.