Study on the effect of methanolic crude extract from barks of Aglaia spectabilis (Miq.) Jain & Bennet on seed germianation and seedling growth of three weeds: Mimosa pigra L., Cenchrus echinatus L. and Chloris barbata Sw. and three cultivated plants: Oryza sativa L., Brassica chinensis L. and Ipomoea aquatica Forsk.. The concentration of crude extract were 0, 0.125, 0.250, 0.500, 1.000, 2.000 g/l.The result showed that the crude extract inhibited seed germination of all three weeds and two cultivated plants: Oryza sativa L. and Ipomoea aquatica Forsk., but had no effect on seed germination of Brassica chinensis L.. It also found that the concentration of crude extract at 1.000 and 2.000 g/l absolutely inhibited seed germination of Chloris barbata Sw.. For the effect on seedling growth, it showed that stem and root length of all six tested species were remarkably suppressed when increasing the concentration of crude extract. It also showed some abnormal morphological symptoms on seedlings treated with crude extract when compared with the control.