Productivity of groundnut (Arachis hypogaea L.) in Bangladesh is very low, due to many limiting factors beset in its cultivation. Plant density and weed competition in crop constitute the main limiting factors. In order to combat the problems, the optimum plant density and most appropriate weeding period for good production in groundnut has been investigated at Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh, Bangladesh. Two plant density viz. 200,000 and 400,000 plants ha-1, and seven weed competition periods from 0, 25, 40, 55, 70, 85 DAS and up to harvesting time were studied. Nineteen species of weeds representing 10 families were found to grow and population density was 150 plants m-2. The major infesting species of weeds were Cyperus rotundus L. (Mutha), Chenopodium album L. (Bathua), Physalis heterophylla L. (Foska begun), Gnaphalium luteo-album L. (Shwetomuli) and Paspalum disticum L. (Knot grass) which constituted about 84.66% of the total weed population. Cyperus rotundus alone shared the maximum relative density (57%) having 85.5 plants m-2 area of total weed vegetation and also shared the maximum intensity of infestation (2.85). Intensity of weed infestation was always higher at lower plant density. Weed dry matter production was higher at a density of 200000 plants compared to 400000 plants ha-1. In contrast, weed dry weight was progressively increased with increasing weed competition period and it was the highest in unweeded plot and critical period of weed competition appeared at 40 DAS. Weed competition period from zero to 40 DAS and thereafter weed free up to crop harvest with a density of 400000 plants ha-1 gave the highest pod yield The pod yield was found to have a significant negative correlation with weed dry matter production i.e. an increase in the dry matter production will lead to a decrease in the yield of pods.