Abstract: Establishment of optimum plant population is an important factor for increasing grain and stover yield in corn (Zea mays L.). The effect of varying times of thinning on the stover and grain yield of maize was investigated in a replicated field experiment, using an open pollinated maize variety Azam, at farmer=s field at Swat, during summer, 2001. Significant differences were observed among the four thinning treatments for grain and stover yield. The grain and stover yield were found to have decreased as thinning was delayed. Yield components such as number of ears, ear length, number of grains per ear row, ear diameter and 100 kernel weight were significantly affected by late thinning. In vegetative phase, LAI (leaf area index) was the only character, which exhibited significant differences among thinning treatments. The results suggested that thinning of maize crop as early as seedling emergence is important for increasing yield.