An experiment was conducted in research station of Isfahan University of Technology in summer 2007 in order to evaluate the effects of row spacing and plant density on yield and yield components of sweet corn, variety KSC403. A randomized complete block design was used with a split-plot layout and three replications. In this experiment the main plots were row spacing (60 and 75 cm) and the sub-plots were four levels of plant density (50000, 70000, 90000 and 110000 plants per hectare). There were significant effects of row spacing on plant height, leaf area index, plant dry weight, numbers of tillers per plant and per square meter, grain weight, grain fresh yield and the percentage of starch, total sugars and sucrose in the grains. Leaf area index, plant dry weight, numbers of tillers per plant and per square meter, grain weight, grain fresh yield and grain starch percentage were significantly increased as row spacing was decreased from 75 to 60 cm. However, plant height and the percentage of total sugars and sucrose in the grains were higher in the plots with 75 compared to 60 cm spaced rows. There were significant effects of plant density on plant height, leaf area index, plant dry weight, numbers of tillers per plant and per square meter, yield components, grain fresh yield and the percentage of total sugars and sucrose in the grains. Plant height, leaf area index, plant dry weight in square meter and the numbers of ears in square meter were enhanced as plant density was increased. However, dry weight of single plants, numbers of tillers per plant, numbers of ears per plant, grain weight and the percentage of total sugars and sucrose in the grains were decreased in the treatments with higher plant population. The number of rows per ear, the number of grains in each row and the numbers of grains per ear were significantly decreased as plant density was increased from 70000 up to 110000 plants per hectare. There were no significant differences between the density of 50000 and 70000 plants per hectare in this regard. There were significant interactions between row spacing and plant density on leaf area index, plant dry weight, number of ears per square meter, number of grains per ear, grain weight, grain fresh yield, the percentage of total sugars and sucrose in the grains and the softness of grain texture. The highest values for leaf area index and the plant dry weight in square meter were obtained in the plots with 60 cm spaced rows and 110000 plants per hectare and the lowest values were achieved in both row spacing treatments in the density of 50000 plants per hectare. However, the highest amount of grain fresh yield was obtained in the plots with 60 cm spaced rows and 70000 plants per hectare and the lowest amount were achieved in both row spacing treatments in plots with the density of 110000 plants per hectare. T