Introduction Several factors affect the crop yield and weeds are among the most important factors reducing crop yields. There are high tendency to develop alternative methods of herbicides for natural control of weeds in organic products. One of the alternative methods to manage weeds is INTERCROPPING. INTERCROPPING is growing two or more crops simultaneously in a piece of land during a growing season. The objectives of the present study were to examine the effect of cereal-legume INTERCROPPING on weeds growth. Materials and Methods A field experiment was conducted in College of Agriculture of Darab, Shiraz University during 2014-2015. In the experiment 16 treatments (five weed free monocultures of wheat (M1), barley (M2), triticale (M3), pea (M4), faba bean (M5), 5 weedy monocultures of wheat (WM1), barley (WM2), triticale (WM3), pea (WM4), faba bean (WM5), and six replacement INTERCROPPING treatments of wheat + pea (I1), wheat + faba bean (I2), barley + pea (I3), barley + faba bean (I4), triticale + pea (I5) and triticale + faba bean (I6) without weed control) using a randomized complete block design (RCBD) with three replicates were studied. Cereals and legumes were planted simultaneously at 23 November 2014. Planting operation was conducted on both sides of the ridges. Weed diversity was calculated by Shannon diversity index: 1 ln s i H N i N i N N N=Total number of plants in each plot of one square meter, Ni= number of species i plants, S= total number of species, and H= Shannon diversity index. This index value ranging from zero to five, higher index value, greater diversity. Results and Discussion The results showed that the lowest density and biomass of weeds were obtained in both sole culture and INTERCROPPING of barley. For instance, the lowest weed biomass was observed in monoculture of weedy barley (1 g. m-2), INTERCROPPING of barley + faba bean (12. 67 g. m-2) and INTERCROPPING of barley + pea (56 g. m-2). The weed density at weed free sole culture of barley (30 plants. m-2) was lowest that followed by barley + faba bean INTERCROPPING (81 plants per m-2). The lowest species weed diversity was obtained in barley + pea (zero) and weedy barley (0. 007), respectively. The weed diversity of most INTERCROPPING treatments was similar or less than that of weedy sole culture. In General, pea or faba bean monoculture had greatest weeds density and biomass, because slow growth and late seedling establishment. However, cereals especially barley controlled weeds properly, due to greater growth rate, higher height and greater density than those of legumes. INTERCROPPING of pea and faba bean with cereals reduced weeds growth and had lower weeds density and biomass than those of pea and faba bean weedy monocultures. In order to increase of legume yields, more density of legume should be intercropped with cereals. Conclusion In general, INTERCROPPING treatments caused a significant decrease in weeds density and biomass compared to the legumes monoculture. In this experiment barley and triticale due to good properties such as fast growth, high plant height and more shading could considerably control weeds in both monoculture and INTERCROPPING treatments, reducing significantly weeds density and biomass in itself sole culture and INTERCROPPING treatments. To reduce the weeds growth in faba bean and pea, which have a poor competitive ability with weeds, INTERCROPPING with cereals, especially barley and triticale, in the south of Fars province is recommended. However, INTERCROPPING is one of the ways to reduce weeds in the long term and its effects on weeds in the long period will be much more. Acknowledgments The authors would like to acknowledge the College of Agriculture and Natural Resources of Darab, Shiraz University, to finance the project and all those who helped us in this project.