During the period 2008-2009 investigation was performed to determine the species composition and density of weeds in the main cereals (wheat and barley). The aim of study was to establish the weed species diversity and the background of weed infestation in wheat and barley in the region. The number of weeds in wheat and barley was established in three regions west, east and south from Stara Zagora by itinerary method in 10 points for each region. Weed infestation and domination of weed species was established by Statistica for Windows. In the eastern region of Stara Zagora (the land of Dalboky) the most propagate weed was Veronica hederifolia L. – 37,2 and Convolvulus arvensis L. – 10,3 plants per m2. In the western area of the municipality (the land of Bogomilovo) prevail mainly Avena fatua L. – 16,4; Veronica hederifolia L. – 12,8 and Galium aparine L. – 6,6 plants of m2. In the southern region (the land of Malko Kadievo) winter cereals have higher weed infestation compared to the other 2 regions. The most propagated weeds in this region were Chenopodium album L. – 36,2; Convolvulus arvensis L. – 7,3 plants per m2 etc. The type of weed infestation of wheat and barley in the investigated areas was as a whole the typical for these crops.