Crop density and spatial arrangement affect the potential of intraspecific and interspecific competition as they increase the canopy light absorption.The effects of the corn density and planting pattern on the growth of common lambsquarters (Chenopodium album L.) was studied in a randomized, complete block design with three replications and factorial arrangement at University College, Aburaihan, Iran, in 2003.The plant density was the recommended density and 1.5-fold the recommended density.The planting pattern treatment also was performed at two levels: one-and two-row planting. The common lambsquarters density was 0, 5, 10, and 15 plants m -1 per row. The results showed that the leaf area index, biomass production, crop growth rate, and inflorescence biomass of the dry matter of common lambsquarters were decreased by increasing the corn density. But, the leaf area index, biomass production, crop growth rate, and inflorescence biomass of the dry matter of common lambsquarters under the two-row planting pattern were less than under the one-row planting pattern, although these differences were not significant.