The study about the effect of weed eleusine indica L. on the critical period of weed-crop competition and effect on growth and yield of mungbean (Phaseolus radicatud L.) had been conducted from March to May 1998 at the plastic house and the Laboratory of Plant Ecology, Biology Departement,Faculty of Matematic and Natural Science,Andalas University, Padang.This experiment carried out by using completely Randomized Design (CRD),with five treatments and five replications.The result of this experiment indicated that the weed in this critical period which weed at first growth of send, infuence of primer branches, while weed at first growth of pods influence to ponds amount,,seed weight, and reduced seed of in amount about 32,72% - 46,36%. While the crisis period it self hoppened at the moment formation at pods, about the fifth week.