Abstract: For studying the effect of intercropping system of onion plants on sugar beet plants, a field experiment was conducted at the Experimental Farm, Faculty of Agriculture, Assiut University which carried out during two winter growing seasons of 2011-2012 and 2012-2013. In the study, we focused on the relative advantage of intercropping systems of sugar beet with onion on the growth, yield and yield components of the two crops intercropping parameters which also considered. The effects of the associated cropping patterns of onion with sugar beet on yield and its components of onion crop were significantly decreased by intercropping. Nevertheless the yield of sugar grown in monoculture was slightly high than obtained from any intercrop combination under study. These results may be due to competition between sugar beet and onion plants for nutrient, water and solar radiation. The highest values of Land Equivalent Ratio (LER) and gross return were observed when sugar beet intercropping with onion as compared to mono crops of either species. This investigation showed that grown sugar beet intercropping with onion gave the highest economic return for the farmers.